A lot of people take great pleasure in hating Taylor Momsen. You can certainly see why she might make her contemporaries jealous. Momsen, aged 17, has already clocked up nine film roles, including Spy Kids 2 and The Grinch, signed to mega modelling agency IMG, and become a teen heroine thanks to her role as Jenny Humphrey, the arty outsider turned snobby superbitch in the TV show Gossip Girl. She is also the face of Material Girl, Madonna's daughter's clothing range. Not bad for someone who has a fondness for saying things like: "I fucked a priest once – just kidding."

So perhaps we shouldn't be surprised to learn that Momsen's taking a break from Gossip Girl to focus on her band: a grungy outfit called the Pretty Reckless. They played New York nightclub Don Hill's the night before our interview, and made for a slightly discomfiting spectacle. Momsen – slender, heavily made up, wearing stockings and a suggestion of a skirt – was flanked by three hairy rockers who looked about twice her age. This rock chick in stripper heels was a long, long, way from Cindy Lou Who, the cutesy character she played in The Grinch 10 years ago.

Momsen sang well but, for all her songs' "rawk" angst, proved a strangely inanimate performer. The crowd's awkwardness only worsened when, mid-song, Momsen pulled down her top to reveal gaffer-taped nipples.

Still, as I wait for Momsen in a Manhattan diner, the image that haunts me is not this on-stage flashing, but her appearance, earlier this year, on ITV's This Morning, meeting Phillip Schofield and Holly Willoughby's softly-softly enquiries with dead-eyed scorn. There's a hilarious bite-your-fist moment when Schofield hastily apologises to camera after she says: "[I] just don't give a shit." Apparently, she had food poisoning, but you get the impression that cosying up to daytime TV personalities isn't high on her list of priorities, whatever her health.

So it's a nice surprise when she slips into the seat opposite me with a cheery: "How are ya?" Even in swathes of maroon eyeshadow and lipstick, she's incredibly pretty – and surprisingly twitchy, plucking at the sleeve of her over-sized T-shirt, gulping her coffee and letting out a nervous laugh.

Momsen, who was born in Missouri, has been in "this business" her whole life. Her first job, at the age of three, was in a Shake'n'Bake commercial, but she's keen to stress that music has always been her main interest. "Everything else I've just sort of done," she says. "It's not that I don't like it, it's just not me." She grew up listening to her dad's Beatles records, but freely admits that, since then, her listening hasn't strayed far from classic rock. Of contemporary music, she says: "It's a very pop-orientated market. There's no real kind of rock'n'roll, there just isn't. So – get angry kids! Listen to the Pretty Reckless!" British fans will get the chance when the UK tour kicks off next week.

Momsen shows me a picture on her BlackBerry of Madonna photographing her for the Material Girl range: "I was, like, 'Well, this is cool.'" Do her friends ever get jealous of her fame? "Well," she says slowly. "I don't really have many friends. I never have. I was always a loner. I was in and out of school so much – so, I dunno, I'm really shy. Which is weird because you probably wouldn't think that. I've got my, like, six best friends, and three of them are on tour with me the whole time so that's awesome. It's not sad or anything for me. I like it."

A cool head for Tampon-gate

As for fame, she says, "it just kind of happens overnight. No one prepares you for that. On Gossip Girl, I was just going to work, doing what I've always done, and then all of a sudden you're like, 'Woah!' But you get used to it. You ignore it – because whatever people say about me doesn't bother me at all."

Really? Yes, she insists. "If you're in high school, or at college, or at work, someone's not going to like you. It's inevitable." And this, she says, is multiplied if you're famous. "But it doesn't mean anything. And when people say, 'Do you care what people say?' I'm like, 'My goddamn tampon string's on the internet – do you think I care about anything?'" She's referring to a photograph taken of her while on stage this summer that ended up all over the web. "It's fucking douchey," she says. "I saw him as well. My dress isn't that short – it's not like you can see my fucking vagina – and the guy gets down on his knees and shoots up my skirt."

Can you think of any other 17-year-old-girl reacting with such resilience to such a thing? When I tell her I'm impressed, she says: "Well, would I want a picture of my tampon string? Nnnnnnnyo. I'd probably say no if I had an option. But, y'know, what you gonna do? It's there."

But don't you take pleasure in being shocking? "Honestly, no. I'm trying not to be shocking." I squeal in protest, mentioning the previous night's onstage flashing incident. "Yeah, because it's in the video! It's an imitation. Doesn't everyone do that? Doesn't everyone recreate their video on stage? I'm serious! And I didn't flash my boobs. I had tape on them. It was a spontaneous thing – there was some tape in the dressing room, and I'd been wanting to do that for a while. "

The video in question – for the single Make Me Wanna Die, which was used in the recent movie Kick-Ass – features Momsen stripping in a graveyard as she walks towards the camera. "It was held up in legal for a long time because I was 16 when we shot that," she chuckles. "We couldn't release it because, yes, I actually got naked."

She rationalises the nudity thus: "It's such a complex song – and the video really reflects the song, in the way that I'd die for this person. And the point is: if you don't do something that's making you happy, you're just working through possessions and shit; you're dying with nothing anyway. So I'm stripping off my worldly possessions and giving them away. And then there's hell raining down, just cause it looks cool."

As Momsen warms to the theme of female sexuality, she starts to sound weirdly ahead of her years. "I'm a promoter of masturbation," she says loudly, making our fellow diners pretend they haven't heard. "Don't sleep around – learn yourself first! Guys do, but girls don't. And that's why girls have so many bad experiences. But you can know your body, know yourself, know what feels good. You don't have to give yourself away just to have sexual relevance. Because I don't think sex is something people should be afraid of. It's part of human nature, so I don't think it should be so shameful – particularly for girls and young girls."

When she moves onto the subject of her last birthday, she begins to sounds more like the teenager she is, gabbling excitedly: "We had cake, although I don't like cake. I like brownies. But actual cake? I dunno. Something about it, too cliche. I was in Paris and they do shots of espresso over ice cream. Oh my god, that was my favourite thing ever."

Momsen was 15 when she joined Gossip Girl. Does she feel older and wiser at 17? "You get more insight as you get older, on everything. I kind of woke up one morning and I was like, 'Oh, I see what's happening, I get everything.'"

Then she stops abruptly. So what is it she gets exactly? "Well, I kind of woke up and was like, 'Oh, I get it, I'm a product.'" Which might be the saddest words ever to pass a 17-year-old girl's lips. But, with typical Momsen nonchalance, they're delivered with a shrug.