"I have to censor myself, which is not an impulse of mine," says Fisher, down the line from her home in LA. "It's literally like D-Day. If the Nazis find out we're coming ... But I understand. There is just this insane interest. People grew up with these characters, so it's their childhoods."
Getting the cast together to read through the script was, she says, surreal: "I mean, can you imagine if they, 35 years down the line, reassembled Gone With The Wind? Not that I'm comparing them," she says, with a spiky laugh. "Or reassembled whatever, it's kind of amazing. Just on the level of, like, what a trip."
Fisher didn't hesitate to take the part, even though it came with the dismaying caveat that she had to lose 16kg, something she has spent the past year doing.
"Well, yeah, they did that on the first Star Wars," she says. "They always hire not entirely me; they always want me minus anywhere between [4kg and 18kg]. In this case I've been very co-operative. If I could've been as co-operative as I am in this situation in relationships, I'd be happily married. But I complied.
"I've learnt over time that you're not supposed to like everything you do. That was shocking to me, to find that out at, like, 30 years old. Well, okay, if I don't have to like it, then, shit, I can do that."
Fisher has made a career of making the best of things. Ask her what she does best and she becomes unusually bashful: "I don't know," she says. "I'm not a lot of things. Ha. But then I'm more of other things."
How about an actress? "Nah, I never really thought of myself that way," she says.
She does a fine line in sharp, witty heroines - Leia, of course, but think, too, of Marie in When Harry Met Sally, where she stole the show.
"I play parts that are very close to me," she says. "I would think really good actors are travellers; they get outside of themselves and play people distant from themselves, with emotions and accents. I can't do that. I'm an archaeologist: I stay where I am and don't get too far afield."
Nor does she think of herself as a writer, although by the time she was 31 she was already a best-selling novelist. Postcards From The Edge, published in 1987, was a comic roman-a-clef that later became a film starring Meryl Streep as sort-of-Fisher and Shirley MacLaine as not-really-Debbie Reynolds. More novels and volumes of memoir have followed. But Fisher bats that idea away, too.
"I'm a certain kind of writer," she says. "I'm a raconteur, an anecdotalist. I think I'm a wordsmith. It's more content and craft than, you know, plots. I get more lost in character."
Fisher's real gift, then, has been in turning the raw material of an often messy and unhappy life into snappy, glittering stories for the page and the stage, where she's performed one-woman shows. As her friend Nora Ephron said: "Everything is copy."
Telling tales about her life has been a sort of talking cure, making bearable everything from her drug-induced psychotic breakdown to the father of her child leaving her for a man - not to mention the time she shared a bed with a friend and woke up next to his dead body.
Making things funny is an antidote to self-pity. "My grandmother took all the charm and romance out of self-pity."
But it's also part of an endless battle to keep herself amused. "There's a part of me that thinks, 'I wish I hadn't told anybody that'. On a lot of it, it's like, 'Oh f***, now I have to talk about ECT [electroconvulsive therapy], or being bipolar again'. But my thing is to say things that no one else will say."
Is there a line between Carrie Fisher the person and Carrie Fisher the personality?
"I've thought about that as well," she replies. "If it is a character, then I am that character.
My mother is who she is onstage and I am who I am offstage - and that's who goes on stage. I don't know which one is weirder."
Fisher told a story in her first memoir, Wishful Drinking, about the moment she was born, on October 21, 1956. While the doctors were cooing over Debbie Reynolds, looking so pretty and peaceful under anaesthetic, the nurses rushed to the aid of Eddie Fisher, who had fainted as his daughter's head emerged.
"So when I arrived," she wrote, "I was virtually unattended. And I have been trying to make up for that fact ever since."
All through her childhood, Fisher tried to understand the world she was born into. Film, it seemed, was as important as real life - whatever that was. And this was especially true for her mother, who had become a star at 19 with her role in Singin' In The Rain.
"I remember when I was, I don't know, 11, she said: 'You haven't seen Rebel Without A Cause?' I said, 'Well, no, sorry! Didn't you help bring me up?' So she let me and my brother stay up late to watch it."
Her parents were famous, but they were also bedevilled by addictions, bad relationships and money troubles. "I discovered fairly early on that it was not like what other people's situation was. There should be a term for what celebrity children go through, which is narcissistic deprivation. The family is organised around the parents or parent and not around the children. The children are what's swept aside by the paparazzi, literally. I could never really be with my mother in public, because she belongs to the public, and as a kid I resented it."
Fisher wrote journals and poems and, she says, "hid in books. I really liked the way everything worked out, to some extent or other, in a book".
People called her a bookworm "and they didn't say it nice". She read classics, Dickens, Dostoevsky, but eventually discovered a kindred spirit in Dorothy Parker. "I decided that's who I wanted to be," she says. "I worked out that, like me, she was half-Jewish, she was five-foot-one, she had brown hair, brown eyes, and then later on, of course, she married a gay guy. But she married hers twice, so I didn't do that. And she was an alcoholic and she was a wordsmith. That was who I admired, and I started writing limericks like hers."
Fisher's friends at the time tended to be glamorous older women: an actress named Joan Hackett, 22 years her senior, and one of her parents' alcoholic next-door neighbours. "I had a really good time with them. They had irony. And I had just a weirdly sophisticated kind of life that didn't give me things in common with other people." She started smoking marijuana at 13, stopping only when the drug turned nasty six years later, on the set of Star Wars.
"It ultimately turned out to be Harrison's pot that did me in," she wrote - though of course that was only the end of the first act in her long entanglement with drugs.
When Fisher was 15, her mother put her in her Las Vegas nightclub act ("I don't care what you've heard," she wrote in Wishful Drinking, "chorus work is more valuable to a child than any education could ever be"). Two years later, Fisher ran away to London and enrolled in the Central School of Speech and Drama, a year of relative normality. Were there recriminations from her mother?
"Yeah. Up until about a year ago." Fisher laughs. "She never got over it, that I had rejected her. When actually it's a very standard thing, if you're going to become your own person."
What did her mother think when Star Wars became a hit? "It's a line from Postcards: 'You want me to do well, just not better than you'. I don't think she knew really how to react, but she saw me as an extension of her, so my celebrity was hers, and she didn't resent it or anything."
These days, mother and daughter live in Fisher's LA compound, along with a rotating cast of boarders.
"It's like a little commune," says Fisher. "That's where I've found myself in my life now.
That's my version of having a relationship. Right now I have three straight guys and one gay man, so that's really a nice little harem. I think about six months ago it was three gay and one straight."
Regular visitors include the singer James Blunt and the novelist and screenwriter Bruce Wagner - whose latest film, the David Cronenberg-directed Maps To The Stars, features Carrie Fisher playing Carrie Fisher. That's Hollywood.
But Fisher values the world outside Los Angeles, even needs it for her sanity. Many of her best friends live on the other side of the Atlantic: Helen Fielding, Graham Norton, Ruby Wax, Stephen Fry. "Stephen's also bipolar, so we had a very manic dinner recently. It was just: try and get a word in - there was no edgewise."
Fisher was once the great advocate for ECT - not that there's been much competition for that title in the past 50 years. The therapy helped with her depression but shredded her memory; she doesn't have the treatment anymore.
Do drugs and alcohol still have an appeal? "Oh God, yes," she says. "I would be riveted to do LSD at this point. I still get possessed by it. I get taken over by discomfort and it's an 'anywhere but here' thing."
Fisher once overdosed accidentally, and she knows she was lucky not to die of her addictions.
"I was a smart person who did stupid things. I got into Alcoholics Anonymous and I liked the principles of it, but I still monkeyed around. I said that I was 'lober' - loaded and sober."
Although she's made great sport of her life, Fisher does get bored with talking about herself. "I'm curious about other people's lives because they're usually very different from mine."
