"I think it is more difficult, losing a man to another man. It's not like you can look at yourself in the mirror and think, hmm, if only I had bigger breasts or a smaller ass." The treadmill hums, Fisher talks through her perspiration. "But that's not the point. I suffered in that last relationship. It was a lot like reliving my childhood. There were lies and deceptions and betrayal."
Then she pauses, the treadmill slows down. "Let's go off the record." That's Fisher's choice when it comes to Billie's father, to protect her three-year-old from recriminations. She will talk about her real feelings towards her ex-lover, talk she loves, talk is therapeutic. But she doesn't want Billie to read bad stuff about her father, because she has seen where that leads. She's been there, Percodan bottle in hand. "I think women are more inclined to blame themselves when a relationship breaks down. It can get out of hand; I don't want that for Billie."
Fisher is ideally suited to her next role, a documentary maker for the BBC, talking about kids in Hollywood and other LA foibles for two hours, the first of which airs on 30 August. Fisher's first photo-call came within two hours of her birth, when the studio PR guys had her posing for Life with her mother, the "adorable Debbie Reynolds".
In her first 10 years Fisher saw her father more on television than in the flesh, although her mother had plenty of other men passing through the house, most of whom were big stars. "I was aware of everybody trying to be witty, trying to succeed and I felt tremendous pressure." By 13 Carrie and Debbie were on stage together and by 19 Ms Fisher became Princess Leia, the perky heroine of three Star Wars movies. She was now a star in her own right.
"When I was a kid people would tell me how lucky I was, to live with film stars." The treadmill churning, Fisher lets out a characteristic shriek. "Hah, I had no idea what they meant. All I knew was that my mother spent hours dressing up when she wasn't sleeping or racing out of the house. To me a movie star was somebody who always smelt good and wore fabulous clothes. When people started to say I was a star I knew I didn't wear clothes with the same grace as my mother. I didn't have her quality, it was a painful realisation."
Fisher asks me about London. She can't understand why I'd rather live in New York. "I'd love to get Billy out of here and into a London school. That way, she'd be less likely to come home at age five and ask if she can have a nose job." Her BBC films focus on these perils, the risks of a Hollywood childhood. "What child is going to say no to the attention? They don't know enough to see how it can destroy them. People here are designed for public lives, there's no true closeness in Hollywood because everybody does the false closeness so well. Kids can't read mixed signals. Children are people pleasers but if they succeed their life is over at 15, they're maxed out but still addicted to all the attention."
Carrie Fisher knows all about addiction. In 1985 she forced herself into a rehabilitation clinic after a drug overdose. The year before, her marriage to singer Paul Simon had fallen apart and the Percodan finally caught up with her. After that she could no longer play perky with conviction. And along came Carrie Fisher, author and screenwriter. It was a tough rebirth. "I had a frightening thing happen," she writes in the semi-autobiographical Postcards from the Edge, her first novel. "I had my stomach pumped. It was a fairly graphic illustration that my way wasn't working." Two more novels followed, both received good reviews. Then there was a grown-up role in When Harry Met Sally. Postcards became a movie and Fisher is now in demand as a screenwriter.
"I haven't acted for six years," says Fisher. "I'm working on a new book which I'm supposed to finish yesterday." In the last year she has also written large chunks of the screenplays for Penny Marshall's New Leaf, for a new Sandra Bullock movie about time travel and for Two for the Road, which will star Meg Ryan. Fisher is now regarded as one of Hollywood's "power writers". "I prefer this job to acting, I don't like my appearance and this is an appearance-related profession. I would write anyway although I do have an added incentive now." She's talking about the huge house in Beverly Hills that she bought for her and Bryan Lourd, the one where right now she pounds the treadmill. "I have a half a million dollar mortgage which I was not expecting to pay for on my own so I have to keep real busy." Huff, puff.
Fisher tries to save the days for her daughter and then she writes at night. "I like to curl up on the couch and smell the night air, then I write until 3 or 4am. I always play music." What sort? She laughs a little nervously. "I'm sure you won't be impressed. I'm trapped in a time warp from when I wrote my last book. I like Tom Petty, Joni Mitchell, kd Lang - oh, and Seal. It has to be fluid and lush. I like songs that should only be sung at night when your heart is breaking."
It's an obvious invitation to ask about her heart. She sighs. "When my father left my heart was broken and that has forever stuck. I have tried to function as a trusting person and I've been nailed. Now it's me I don't trust. It's when I look at somebody and say `oooh', that's when it becomes dangerous." Did she go "oooh" when she first saw Bryan Lourd? "Now I said we weren't going to talk about that. I picked him and I'm accountable. It's a nightmare to live in a world of blame and accountability." She laughs, it's half serious and half a joke. That's Carrie, still perky after all but now an institution as well, able to coax the Hollywood gods to chatter for the BBC.
"I'm Hollywood's observer," she says. "The only reason I have this position is because I respect the cult of celebrity too much to violate it, I can't violate a hard won trust. I know how painful that can be. People know most of their secrets are safe with me."
The treadmill stops. "I do this every day," she pants. "I do 52 or 54 or 57 minutes, those are my lucky numbers. Roseanne's is number five. We both suffer from obsessive/compulsive disorders." Roseanne Barr is one of Fisher's best buddies. Barr recently asked Fisher if she would take the part of Edina in the US version of Absolutely Fabulous. According to the media, Fisher has taken the role. "No I haven't, where do they get this crap!" she says. "I thought about it, but I have so many other projects and they won't start shooting for six months. I have no idea what I'll be doing, except that I know I'll be looking after Billie."
Billie is named after Billie Holiday, Billie Jean King and Billy Burke. "One was a junkie, one isa lesbian and one just a sweet woman. In case she doesn't want to be any of those three I called her Catherine as well." Billie Catherine, the daughter she's now trying to protect from Hollywood. "I don't let Billie watch television. I want her out of here before she goes to school. Once you send the child to school you lose control. The cake is baked at five. It makes me very careful about what I expose her to."
Even now Billie is noticing the oddities of her environment. "Billie is only three so she thinks its normal that her mummy lives in one house, her daddy in another. The other day we went to Meg Ryan and Dennis Quaid's house. Billie noticed that they lived in the same house and she found it extraordinary."
So how does she cope with this empty father space in Billie's life? "It's not empty. We go to the child psychologist together. So long as we are good to her, so long as we are nice to her. That's the best we can do, that and we must not go to war with each other. That's what my parents did and it was fantastically destructive."
Fisher claims her books are about "the spaces between people" but all three of her novels are mirror images of her life. In the third, Delusions of Grandma, the heroine is a single mother called Cora who rewrites screenplays. Her mother Viv has moved beyond her Hollywood career and owns a hotel. Debbie Reynolds now owns a hotel in Las Vegas. After falling out when Fisher portrayed Reynolds as a drunk in Postcards, mother and daughter have reconciled and Carrie has invested in mum's new project. Can she write about anything but her own life? "I will have to, the fourth book will not be about me and Bryan playing shuttlecock with Billie. I'll spare her that."
So has Carrie Fisher obliterated the death star which once threatened her peace of mind? I call her the next day to find out; she's back on the treadmill. "I know my likes and dislikes now," she puffs. "I don't like exercise but I do it, I like drugs but I don't do them. I like reading, I like my therapist. I like food, I like Buddha and I even don't mind AA. I like Meryl Streep because she's talented and she has four children and a husband and she does them, she doesn't juggle them. I admire people who strike a balance between showbiz and a useful life."
That's hard to do when your DNA reads like the Hollywood sign. "It's not really as hard as I make out," says Fisher. "This BBC thing was a breeze. I just got together some of my buddies here and we went off on the place but every one of us is still in love with the glamour and the gossip."
That's Fisher. Once just perky, now perky and real with a child and a sense of humour, a treadmill and an AA programme. A survivor. "You can either resent the emotional wreckage around you and sink beneath the waves, or you can strap it all together and make some kind of lifeboat." The treadmill whirs on.