Kristen Stewart started auditioning for movies when she was nine, but she has never looked anything but uncomfortable in her daily role as a star. Right now, surrounded by journalists in Cannes, she is faintly grouchy and very twitchy, as if she would like to wriggle out of her skin and leave it for us to pick over while she slithers off under the nearest door.

And who can blame her?  When she won the role as Bella Swan in the first Twilight film, she says everyone expected it to be a small film for genre fans  In the end, the four films in the franchise grossed $US2 billion. In 2011, Forbes magazine calculated that for every dollar Stewart was paid, she brought in more than $US55 – a heavy financial responsibility at the age of 21. Meanwhile, paparazzi monitored every move she made with Robert Pattinson, the vampire lover who also became her real-life boyfriend.

In her new film Clouds of Sils Maria, Stewart plays the personal assistant to a famous actress; one of her innumerable tasks is to minesweep public places for paparazzi. Thus the first Cannes screening ripples with laughter when Stewart scouts Zurich railway station, pronouncing it clean by saying, "The cockroaches must have taken a later train". She laughs about it herself. "It was a lot of fun to be the one to say that," she says. "It wasn't a statement about anything to do with my life, but I was just like the perfect person to say those words. You know what I mean? Because I obviously have a lot of experience with that."

Of course, the fact the Twilight stars were embroiled in real life was a story made in tabloid heaven. Two years after they split up for the second and final time, it's still running:  Stewart's supposed negative opinion of Pattinson's current girlfriend FKA Twigs is a regular headliner.  Her own romantic status is unconfirmed, but rumours swirl about her relationship with Alicia Cargile​, who – ironically enough, given the character Stewart plays in her new film – is her own former personal assistant. So far, the only real evidence is some pap-snapped hand-holding and somebody's observation – possibly erroneous – that they have matching tattoos. The idea that Stewart's real life is once again echoing her life on screen, however: that has to be good for a story.

In every other respect, though, Clouds of Sils Maria is about as far from the Twilight franchise as anyone can imagine. Written and directed by French auteur Olivier Assayas​, it stars Juliette Binoche as Maria Enders, a venerated actress who, against her own immediate inclinations, has agreed to star in the play that made her name more than two decades earlier. Back then, she played the role of a brash young woman who seduces, then abandons, her much older female boss.

This time around, she will play the boss's part while a new star from a superhero franchise (Chloe Moretz) will replace her as the young temptress. The prospect makes her feel old, while watching those superhero movies makes her feel artistically irrelevant. The greater focus, however, is on her devoted assistant Valentine – played with marvellous restraint by Stewart – whose own insecurities are buried under endless work; she spends her life with a phone to her ear.

Stewart likes the way Assayas has nailed details she recognises of celebrity life. So are actors really so fragile? She thinks so; it comes with the creative territory. "Most people aren't born with this impulse to write or, like, make shit out of clay or with this impulse to do performances," she says.  "Some people are just happy within their lives having families, having work:  you know, that's like satisfying for them. So I think that unique thing definitely, commonly goes along with having something to protect, because you are different and a little weird. I think I am definitely insanely sensitive. Just ridiculously."

Even so, she has managed to tough out the Twilight years, sliding with apparent ease into a spread of independent films and another fairytale blockbuster franchise, Snow White and the Huntsman.

"I think the reason I don't get swallowed up by the Hollywood machine is that I really like to think," she says. "And I really like to make movies; I just really want the experience of it. Most actors – not good ones – don't do things for the experience of it; they are just really product-oriented. As is the business, which is why when things are good they stick out."

Her theory on celebrity culture is that it serves stars up in much the same way that Hollywood films package stories. "They're all easily consumable and fun."

That doesn't mean she doesn't want to do Hollywood films, however. "I still like big American big-budget movies – that's my foundation, that's what I grew up on. I don't want to be 'oh, I only do artsy movies now'. And also within the whole packaged thing, it is possible to make really good movies."

Stewart is also keen to direct her own films. "I have never been comfortable saying that. I have worked with too many amazing people to comfortably say that. But it's never going to happen unless I start thinking about it now, so I'm going to start dinking around and making shorts."

One day, she says, she would love to be back in Cannes with a film of her own. She may find stardom uncomfortable, but Kristen Stewart knows exactly what she wants.

Clouds of Sils Maria opens in cinemas on May 7. 

Life after Twilight

"I didn't make a movie for a two years because I didn't have one that I liked," says Kristen Stewart.

"That was not a plan. I was just like dying. I was like 'where is it, I can't find it?' Sometimes you can read a script and it can be fantastic, but that doesn't mean that it's in you to play it. Even if you're right for the part, you fit the description, doesn't necessarily mean that it's in you."

After Twilight, Stewart played Mary-Lou in Walter Salles' adaptation of Jack Kerouac's On the Road;  a guard at Guantanamo Bay in Camp X-Ray; and Julianne Moore's daughter in the Oscar-winning drama about Alzheimer's, Still Alice. Forthcoming projects include films – so far without titles – with Woody Allen and with Meek's Cutoff director Kelly Reichardt​. She is currently filming a drama set in the Iraq war directed by Brokeback Mountain's Ang Lee. Just announced is a forthcoming retelling of the story of Bonnie Prince Charles, with Stewart playing Flora MacDonald.