Dakota Fanning as Jane Volturi in 'New Moon': 'Kristen Stewart being scared of me was kind of cool'

It's 10am on a Saturday and Dakota Fanning is showing off her favourite shoes. The 15-year-old Hollywood starlet is snappily dressed in blue jeans and a chintzy white top, and with her baby blue eyes and slightly crooked smile, she looks very much her age. "Aren't they cool?" she says, beaming, directing my gaze towards her feet.

The shoes look enormous, and they're also a striking purple colour. Even though they carry the mark of fancy shoemakers Marni, some might even call them ugly. "Actually, some people hate them a lot," she says with a laugh. "I have had them a long time. I love shoes. I love high shoes. They are so ugly, but I just love them. I wear them every day, to school, everywhere."

Unlike the majority of her peers, though, Fanning gets to wear her best shoes not just to school but on the red carpet. Despite her tender years, she has now worked on more than 20 projects – including heavyweight films such as I Am Sam (2001), Man On Fire (2004) and War Of The Worlds (2005).

Her CV is about to get another boost with her forthcoming role in New Moon, the sequel to last year's vampire smash Twilight, adapted from the novels of the same name by Stephenie Meyer. Fanning plays Jane, a member of the Italian vampire clan known as the Volturi, and she emerges as the nemesis of the series' heroine Bella Swann (Kristen Stewart).

"My character is kind of evil and mean," she says, laughing. "I have to have these red eyes which are kind of scary-looking, and some really cool scenes. There's one involving me and all the main cast, and all the other Italian vampires. I wasn't required to do anything really physical but Jane really wants to get Bella, who just kills my character." But only metaphorically, right? "Right," says Fanning. "Jane wants to cause Bella pain so badly and that's weird because I am really good friends with Kristen in real life now. To be mean to one another is strange, although her being scared of me was kind of cool."

Fanning was midway through reading Meyer's Twilight series when she got the call about the film. "That made reading the parts about Jane really fun when I knew it was going to be me," she chirps. "I think these films are really for everyone – kids and adults alike, boys and girls."

With Twilight's enormous haul at the box office (worldwide tally now approaching $400m – a figure the producers will hope to double with DVD sales), that's a reasonable assumption, although most viewers would concede that the Twilight saga is skewed towards a female, teen audience.

Just a few days after we meet, Fanning is heading off to begin work on Twilight's third instalment, Eclipse. "It is getting a bit like a big family," she says, grinning.

She has certainly bonded with Stewart, the saga's leading lady. Not only did the two form a relationship on set, they continued working together the moment New Moon finished filming. In fact, just the evening before I sit down with Fanning, she has completed the main photography on The Runaways, a big-screen biopic of the iconic 1970s girl band of the same name, fronted by Joan Jett. Based loosely on the autobiography of the band's lead singer Cherie Currie, the film adaptation sees Stewart step into Jett's leather boots and Fanning into Currie's.

"Last night Joan Jett gave me a scarf and I love it," she says. "To me, something like that is important because it's a gift from someone I really look up to."

Fanning clearly looks up to Stewart, too. "Kirsten is just the coolest person ever. When I watch her work, I see how much she cares about the part she is playing and how much she wants to get it right. With this film there was so much to live up to as they [the Runaways] were such incredible people in real life. Clearly we're never going to be as amazing as they were," says Fanning, "but you try your best and Kristen was putting everything she could into it. I think it's brilliant work."

Stewart has clearly had an effect, which actually makes perfect sense. The older actress (Stewart is approaching the heady age of 20) is incredibly bright and must come across as being exceedingly cool, especially when you're a 15-year-old girl. And, of course, the pair have plenty in common. Both were child actors. Fanning cites Jodie Foster (one of Stewart's mentors, from her first movie Panic Room in 2002) as the actress with whom she most wants to work. And she says that she's been called "an old soul" – which is how Stewart also frequently refers to herself.

Fanning's big-screen breakthrough came eight years ago, in the 2001 Sean Penn and Michelle Pfeiffer movie I Am Sam. It proved a real boon for the then eight-year-old actress, making her the youngest person ever to be nominated for a Screen Actors Guild Award. She has gone on to appear in movies as diverse as Hansel and Gretel (2002), The Cat in the Hat (2003), Hide and Seek (2005), Charlotte's Web (2006) and The Secret Life of Bees (2008). She is now, it seems, approaching womanhood with her career and her life very much on track.

Fanning was born in Conyers, Georgia, the daughter of Joy, a tennis professional, and Steve, a former minor-league baseball player with the St Louis Cardinals. She began acting at the age of five after appearing on a television commercial for stain-removal specialists Tide. Her first significant job came with a role on the US prime-time drama ER, while she also made several guest appearances on television series such as CSI: Crime Scene Investigation, Friends, The Practice and Spin City, and portrayed the title characters from both Ally McBeal and The Ellen Show as their younger selves.

Much of her education unfolded in private, on film sets, although she has now joined Campbell Hall School in North Hollywood, California, and is on the cheerleading squad. And then there's religion. "My family is Christian and I am Christian and I go to church," she says. "It's a big part of my life." She lives at home with her parents and her 11-year-old sister Elle, who has also taken her first steps along the acting trail. (She performed as the young Cate Blanchett in The Curious Case Of Benjamin Button last year.)

"I love my sister," says Fanning when I ask about sibling rivalry. So that's that then. Or maybe not. "I have this blue blazer that I really love. I wear it to school all the time. It is my favourite thing. And then I noticed it was missing. She [Elle] is very tall so we can share things but one day it was gone. I thought it must be at the dry cleaners so I didn't freak out. Then we picked her up from school and she was wearing my blazer... I recognised the gold buttons. I was like, 'No, you just do not do that.' And now I come home from work and I'll see all these clothes in a pile and think, 'I didn't have all those things out.' She has started to steal my outfits."

The tabloids have already welded Twilight's two leading actors, Stewart and Robert Pattinson, into a potential item, and Dakota Fanning will no doubt come under the same type of pressure, especially as she approaches 16. She can already cite a "dumb story" in which it was reported "that I always carried a book of baby names around with me".

Really? So where did that come from? "I do love names and I did have a book of baby names when I was younger and I would go through all the names and wonder what it would've been like to be called so-and-so," she says. "I would put a tick if I liked a certain name and a cross if I didn't. I still have the book, but I don't carry a book of baby names. I can categorically deny that rumour.

"Now, a rumour about my shoes," she says, casting her eyes at her purple Marnis once more, "that would be much more fun."

'New Moon' is released next weekend