Kristen Stewart - The Twilight zone

Kristen Stewart's role as Bella in the films of Stephenie Meyer's vampire novels have made her a superstar. Lesley O'Toole meets the teen sensation

She might have ousted Miley Cyrus from her mystifying position as The World's Most Famous Teenage Girl but Twilight star Kristen Stewart, 19, is in denial. "People don't really recognise me," she smiles, knowing it sounds unhinged. "I think I just look different in person or something. I'm also not very approachable." She laughs hard and knowingly. Take the outfit she wore to this month's Teen Choice Awards (where she won Best Actress Drama for Twilight): a Rock & Republic dress, the skirt section of which comprised only silver spikes. It didn't take an expert to deduce the message: "Don't stand so close to me!"

Stewart has already earned a reputation in the media for being difficult, but it seems a rather uncharitable label. In my three meetings with her, she has been fidgety, yes, uncomfortable, check, awkward, always, but never rude, dismissive or arrogant.

"I do feel that nowadays everyone perceives you the same way," she says, pondering a Facebook/Twitter age in which she does not participate. "I prefer something I can touch! But now everybody knows everything about you. Even your parents have to know where you are because of course you have a cellphone. They can always reach you. You can't even have a private life away from your family, it's like everything is very hands-on."

Her long-sleeved black shirt and dark, skinny jeans seem designed to attract minimal attention rather than fashion points. "I just saw this on a rail." She has accessorised with her own stuff – a black leather wristband, rings on half her fingers and a vintage men's watch. "Fashion isn't something I think about a whole lot and it's such a large area of the media. It's weird."

Greg Mottola, best-known for directing 2007's Superbad, wrote and directed Stewart's new film, Adventureland, a paean to his own teenage years and one in particular, the summer of 1987, when he worked at a creaky old amusement park. Stewart is the outwardly confident, inwardly tormented teenager Em who forms an unlikely relationship with Jesse Eisenberg's James. Mottola says the girl in his story "needed to be complicated and truly conflicted. We needed an actress who can convey a really believable sense of strength. I knew with Kristen that character wouldn't just be a brat.

Ask her about her approximation of an Eighties teenager in Adventureland (she was born in 1990) and she is quick with a response which might look snotty in print but is not delivered that way. "Well, I've never met a terribly introverted damaged girl at a theme park in the Eighties. But I could imagine what it'd be like to not like yourself very much and not have a mum and dad to reassure you and sort of be kicking it alone. To feel like you're sort of smarter than everybody but no one gets it."

Hollywood does get her and doesn'tbother that Stewart's awards to date have been voted for by Twilight-obsessed teens and tweens. Variety's review of Adventureland mused "Stewart impresses again" while the Los Angeles Times termed her performance "equally good as the ethereal Bella in Twilight". Revered American film critic Roger Ebert noted with a certain gravitas: "Here is an actress ready to do important things."

Certainly Stewart likes the choices afforded her by Twilight and is too smart to complain about any downside. "It's easier now to do things I really like, like an independent movie that nobody sees. Now it'll be: 'Oh, let's go see Bella in this stripper movie!' It'll be crazy." She laughs hard, like she's loving it. The "stripper movie" in question –Welcome to the Rileys, starring The Sopranos' James Gandolfini and last year's surprise Best Actress Academy Award nominee Melissa Leo – is one she terms the "most fruitful life-changing movie experience I've ever had. It was the hardest subject-matter. I play a very broken young girl working in a strip club."

In another film of hers awaiting release, The Cake Eaters, her character has Friedreich's ataxia. "It's a total deterioration of your muscle control, a very debilitating disease. She's just about to be in a wheelchair and is fighting for that last bit of independence from her mother. It's an optimistic, triumphant story." And next year she will star as Joan Jett in Runaways, based on rock icon Jett's teen girl group.

Stewart started acting at nine and insists there was "never a grand plan", either to pursue a film career (her parents are both in the business) or to manage it once begun. Her Australian mother Jules is a script supervisor preparing to direct her first film K-11 (starring Stewart), her father John a TV producer. When a talent scout spotted Stewart in her school's Christmas play, her parents grimaced.

"They said, 'We don't want to be stage-mums'," recalls their daughter with a smirk. Her father was particularly dispirited at the prospect. "He was a stage manager then and was like, 'oh my God, I don't want my kid doing this'."

Their contrary pre-teen was having none of it. "My parents were reluctant and I think I just remembered thinking: 'Actually that might be really cool. I might want to go on a few auditions. I might work.'" She auditioned relentlessly for a year without booking a single job. "It took a really long time until I was totally over it and then came my last audition. I went to it and I didn't even want to. My mum said: 'Well, this is the last one. You don't have to go to any more.' And that was the first movie I got."

The Safety of Objects, released in 2001, starred a veritable Who's Who of leading ladies sure to make an enormous impression on a wide-eyed nine-year-old, including Glenn Close and Patricia Clarkson, who played her mother. The following year Stewart won the role of Jodie Foster's daughter in Panic Room, an experience which cemented her belief she was doing the right thing.

"I think being 10 years old on one of my first movies and spending a month on it with Jodie Foster had an enormous effect on the way I work, probably unbeknownst to me at the time. At least in retrospect, I noticed it. Jodie Foster is the only one who totally shines out in my mind who really taught me a lot."

When she was 12, and working regularly, Stewart left school to be homeschooled by her mother. "I loved it. Independent study is for me." She worked consistently throughout her teens in films from gritty independents like 2004's Undertow opposite Jamie Bell, the Jon Favreau-directed comedy Zathura: A Space Adventure, horror film The Messengers and then 2007's Into The Wild, Sean Penn's mellifluous film version of Jon Krakauer's profound book about Christopher McCandless.

On film sets now, Stewart – like Twilight co-star Robert Pattinson – is delivered from take to take under a gigantic golf umbrella to deter paparazzi and fans alike. The call-sheet from those sets, the one delivered daily to the cast and crew employed on a film, lists her under a pseudonym. And she cannot set foot in public, particularly with Pattinson, without the event being disseminated in its entirety from teen fan-sites to snarky grown-up publications.

Do she and Pattinson ever compare notes on the Twilight phenomenon? "The funny thing is we haven't really talked about it. Although we can commiserate and be like, 'ugh, it's crazy'."

The second Twilight film, New Moon, is released in November, and Stewart is excited that it will be "more tragic". But mostly, she is excited at her character's progression. "Over the course of these four movies Bella has to change. I'm not ruining it for anybody in saying that she and Edward end up together. In the first one he's very much a man and she's very much a child so she needs to become a more formidable partner. We're working on that."

The evolution of Kristen Stewart is also a formidable prospect.

'Adventureland' is released on 11 September