Yet even while struggling with laryngitis ('I'm so glad this interview isn't on video', she says), and now aged 70, her enthusiasm for her subject remains undimmed. Right now, she's talking about Elvis because he would have turned 80 this year and there's a new album out to mark the anniversary. If I Can Dream: Elvis Presley with the Royal Philharmonic Orchestra takes 14 Elvis songs to Abbey Road and freshens them up with orchestral oomph and the odd guest vocal. It's a revamp that Priscilla hopes will put Elvis in touch with the 'young folk', although unless I've woefully underestimated said young folk's appreciation for Michael Bublé (he duets on Fever), I'd wager that the rich, classical setting is more suited to established fans intrigued to hear a fuller-sounding Elvis. Still, Priscilla says it's a testing of the water, to see how people might feel about pushing the boat out further in future.
'I'd like to mix him with other songs', she says, 'like they're doing now with these dance DJs. What do you call them? When they mix two things at once? E, L …'
EDM?
'Yes!' she says, her face lighting up. 'Again, it would have to be very right'.
The image of an electronic dance music Elvis might have purists' heads exploding, but if anyone knows what kind of music the King would be making at 80, it's Priscilla. She was there when he first picked out the songs on these records - 'and there when he threw songs against the wall because the label wasn't giving him what he needed', she adds. One of the songs on the new compilation, An American Trilogy, was proposed by Priscilla herself when she heard it while driving down Sunset Boulevard and thought it would be perfect for him, although she admits that suggesting songs to Elvis was a delicate business. 'You didn't just walk up to Elvis and say: 'Hey, sing this song'. You could maybe suggest something'.
It wasn't just songs that you had to tiptoe around. Elvis could be unpredictable, famous for brandishing his .357 Magnum and shooting the TV if something appeared that angered him.
'It's funny now', she says. 'But scary at first. Very scary. There was no warning. Maybe he was in a bad mood that day, or maybe he would just see someone he didn't particularly care for so he'd just pick up the gun and …' She laughs, a little nervously.
Reading Priscilla's account of their marriage - which lasted from 1967 to 1973, and is documented in her 1985 book Elvis and Me - gives a rather conflicting impression. She seemed very much in love with him, still does, but also admits to being under his control. As the king of rock'n'roll, Elvis was a man who was used to getting his way - and nowhere did he exert this power more than on his wife-to-be, moulding her into his ideal woman by deciding what she wore (block colours, no prints), what she did (she was banned from working), and what interests she pursued (only those in which Elvis was interested). It sounds awful, but Priscilla says that she didn't hate it, it was just their way of life.
'At that time I just liked that he was paying attention to me. He was very opinionated on what he wanted: 'I don't like you in that colour. Brown isn't good for you. Green looks horrible, it's a dull colour with no spark to it'. I was a young kid, 16 years old, so I thought: 'Oh, OK!' It wasn't until I got a little older that I started developing things that I liked'.
Elvis' requirement for perfection sounds exhausting. He kept her away from Hollywood, where rumours persisted about his numerous affairs with leading ladies. He criticised her posture, ordered her to have dental cavities filled and could appear horrified at so much as a bit of cracked toenail polish.
'I remember sitting down doing my homework', she says, a disquieting sentence in itself. 'And when I would look up at him, he would slap me on my forehead and say: 'Don't do that, it gives you wrinkles on your forehead'. I didn't even think about wrinkles back then!'
Were these attitudes a sign of the times? A reflection of his conservative upbringing? Priscilla thinks those things played a part, but that his ideas were mainly taken from Hollywood: 'From stylists and makeup artists … and he watched all the great films'.
There is a particularly disturbing scene in her book when, suspecting Priscilla of having an affair, he ordered her upstairs, and forced himself on her, saying: 'This is how a real man makes love to a woman'. It's hard to read and not get the impression that this was sex without consent, but Priscilla won't elaborate.
'I don't want to talk about that, I really don't', she says. 'I don't want to bring something up that's gonna … just tell them to read the book! Elvis and I had a truly loving relationship, I have to say. I'm not going to taint it in any way. I was honest in my book but people go further, they try and pick out things that make it bigger and complicated'.
Today, she says, she would rather talk about the music. She talks about the first time she saw him play live, when he made his legendary '68 Comeback Special on TV, shortly after she had given birth to their only child, Lisa Marie. 'I was in the audience and I looked at him and thought: 'Oh my God, I had no idea!' she says, laughing. 'I thought: 'He's really good! He's really sexy! Oh my God!'
Later, during Elvis' Vegas residency, where he sold out 636 consecutive shows, she recalls him coming out onstage and stalking the audience 'like a panther, back and forth. Magnificent. The audience were captivated by him. He was so confident, but vulnerable, because he never took his audience for granted, he always wanted to be accepted'.
Elvis spent much of his career frustrated artistically, from his phase in Hollywood making movies he thought were trash, to the Vegas shows themselves, in which he felt hemmed in by an audience that wanted to hear Hound Dog and Blue Suede Shoes every night. Occasionally, he would stand firm against the commercial wishes of his label and management. In the Ghetto, which appears on the record adorned with swirling strings, is one such example: 'Colonel Parker told him never to get involved in two things: religion and politics. He said it's not your genre, you don't want to be a messages singer. But Elvis put his foot down and look what happened'.
One of the reasons Priscilla is proud of If I Can Dream is that all the songs are ones Elvis picked for himself, and that showcase his range of styles, from the melodrama of It's Now Or Never, here boosted by Italian pop trio Il Volo's operatic backing vocals, to the soulful country rock of Burning Love.
'Rock'n'roll was a big part of Elvis, but he's so much more than that', she says. 'For him, there were no barriers in genres of music. If you were good, and it struck him, or he felt something towards the words of a song, he would put his own take on it'.
Does she ever have the urge to put her own take on any of his songs. Does she have an Elvis karaoke song?
'No, never!' she exclaims, horrified. 'Are you kidding? I'm not a fool! I did sing Trouble at the panto, when I was the evil witch, but karaoke? With everyone watching … critiquing … pointing … laughing, more like it'.
You sense that Priscilla has always been wary of being the centre of attention, while at the same time being constantly drawn to it. On the one hand, she was the ultra-glamorous wife of the world's biggest pop star, making herself stand out with her beehive and those cat's eyes, an overdose of eyeliner that inspired countless looks from Amy Winehouse to Lana Del Rey ('I've seen her, it's sweet, really sweet', she says, a little unsure whether she should be taking the credit). On the other hand, she often lived almost in hiding - donning a wig and disguise to look for wedding dresses, or being ordered to stay in the house away from the cameras, especially during the early stages of their relationship when she was still 14.
'We were very careful. I wasn't out in public really. Nobody really knew'.
Does she look back on it and think that it was a little ... strange?
'Knowing Elvis, and his kid spirit and his boyishness, no I don't. I think it would be strange if it wasn't Elvis'.
She says her family had met him, and his father and grandma, before giving her permission to move to Memphis from Germany, where they were stationed at the time. 'My parents felt safe, and they should have done, because Elvis was very respectful of me, he knew how old I was'.
She says Elvis' father, Vernon, was also concerned, although it doesn't exactly sound like he had her interests at heart.
'He was worried that it would be another story like Jerry Lee Lewis, where he married his 13-year-old cousin and that was the end of his career', she recalls. 'He kept reminding him about that'.
Does she feel she lost her teenage years?
'Yes', she says, instantly. 'Yes, I did. There's no doubt about that. But was it worth it? It was so worth it. I missed my teenage years but I was in a whole other life that was scarier! A lot of adults to hang out with'.
It sounds intimidating.
'I was shy. But I'm an observer and always watched to see how people interacted, how they handled or didn't handle things. I learned a lot in that world. Things to stay away from'.
There were plenty of steep learning curves, from Elvis' dabbles in philosophy to working out how he liked his food cooked (burned, basically). One memorable moment involved a dalliance with the world of psychedelic drugs.
'It was Timothy Leary everything at the time', recalls Priscilla. 'Elvis had read about LSD in the paper and how our teenagers were on it and he had this curiosity: what's happening? What are the youth on? So we made an agreement that we would take one tablet, cut it in four, with [music industry associate] Jerry Schilling and I believe [hairdresser] Larry Geller. We had our security around us because we had no idea what to expect. And it was pretty powerful, it scared all of us. We were thinking: 'Oh my god, this is not good!' A total loss of control'.
As Priscilla became more aware of her adulthood, the couple grew apart. Despite being under his instruction for so long, she was single-minded enough to know the relationship was holding her back and that she wanted out. The couple remained friends, though, even holding hands as they left the divorce court in 1973.
It was an amicable split, with the pair sharing custody of Lisa Marie - Priscilla thought it was vital that she knew her dad. Today, the two women are close, and she talks about them competing over who can sink the most Guinness (she claims she can drink eight or nine pints at once). But they had struggles while Lisa Marie was growing up, and there was tension when she decided to marry Michael Jackson in 1994, around the time the singer was engulfed in child abuse allegations. I imagined that, for Priscilla, seeing her daughter getting hitched to the biggest pop star of her generation must have felt like history repeating itself, but she says she never saw it like that.
'My thinking was entirely different. I never compared him to Elvis … they were musicians, and at the top of their game, but I looked at it from being a mom. I was concerned about their relationship. You know, I just didn't know if it was authentic or not. I just worried about if she was doing the right thing. I worried about … his agendas'.
Did she meet Jackson often?
'A few times. He was sweet. But I think he was a bit nervous of me', she says, adding with a laugh, 'Well, I'm the mother-in-law!'
There is something wonderfully grounding about a mother-in-law gag thrown into a family situation that involves two Presleys and Michael Jackson. But Priscilla probably craves a bit of grounding in a life that never lacks surreal moments. In July this year, the same entertainment company that staged a hologram of Jackson at the 2014 Billboard music awards revealed that it was working on one for Elvis too, with plans for a series of 15 live concerts in Vegas next year.
'I have mixed emotions about it', admits Priscilla. 'Using someone else's body with his head, the things they can do today are not authentic … I'll probably get in trouble for saying that! I don't want to put it down before I've seen it but the idea is a little … creepy'.
Priscilla says that revisiting his old records can produce mixed emotions, too, although she is most comfortable when working on projects she knows he'd be comfortable with.
'My mind goes 'Am I doing the right thing?' But then I think: 'Yes, yes, I am. I know I am'. It's as if Elvis is guiding me. I'm being guided by this energy'.
She has talked in the past about being able to sense his spirit. Can she communicate with him?
'It's more … his spirit is communicating to me. When I go to Graceland, my gosh, I can walk in that door and see him walking down the stairs, I can hear laughter, I can hear the music playing in the music room. It's a very surreal feeling. But it's not scary, it's beautiful'.
Along with Elvis' beyond-the-grave guidance, which she claims even members of the Royal Philharmonic Orchestra could feel, Priscilla says two other things convinced her she was on the right track with this current record. One was meeting Elvis' '70s band leader, Joe Guercio, in Memphis shortly before his death at the beginning of this year, and hearing him say that this was a record Elvis would have loved to have made. The other was a call to the Graceland archivist Angie Marchese, in which Marchese revealed the true diversity of Elvis' personal record collection: not just Duke Ellington, Dean Martin, Otis Redding, Patsy Cline and the Ink Spots, but also Royal Philharmonic staples such as Beethoven, Mozart and Brahms. Do many people know Elvis liked Mozart?
'No! Even I didn't know that! I knew he liked Jan Peerce, who was a tenor. I knew he loved Mario Lanza, because he watched The Student Prince I think seven times. He loved opera, because it was drama, it was peaks, lows and highs. But I didn't know he liked Mozart and Brahms'.
This diversity, this artistic lust, is one of the things she'd like to stress most about Elvis: 'He was an artist in the truest sense', she says. 'He'd have loved to have more of an orchestra on his original records, but they - his management, his label - put constraints on him'.
And as in art, as in life, Elvis was a man who didn't really do constraints.