Oh don't people always think they're mature when they're in their teens?! Some changes in the hormones and one taste of the world and they think they know everything.
I don't know if she's lying, 'cos there're so many made-up stories on the Net, especially when BoS is a place for jokes as well...but if she's telling the truth, then there's a whole new issue:
Why do some girls still choose to give themselves when they're from a traditional family? I myself made that choice to emancipate no one else but me. I find that strict moral codes aren't always the best. Let the kids know that they're free to choose, but if you really want them to save themselves for the right person, don't just push the rule onto them, tell them the benefits. If all the benefits sound icky, then you just have to leave them be. The damage has been done.
I frown upon people who save themselves for marriage as much as those who do it just like that with everyone...especially when they're in a steady, deep relationship. If it's your choice, fine...but if you're doing it so just to be above everyone else, let it go! Virginity does not ensure a pure heart. Marriage does not ensure that you've found the right person, or in other words, they rank second. You might never marry the love of your life...you might just regret not having had the experience with them.
To me, you just have to find the right person and go with the flow. You should know where to draw the line otherwise and I think that's where most parents go wrong, if they're traditional. Instead of talking about it and facing it, they turn their backs and bury their heads in the sand, hoping that by not permitting it, it wouldn't happen...but the world doesn't work like that. If your daughter chooses to do it with a long-term partner, then of course it should be fine as long as they're willing to take responsibility and their actions show it. It would not turn her into a slut or anything near it, if it's loving and long-term.
The girl here obviously comes from a strict family, but strict doesn't necessarily mean moral or good. It just means there're things, which may be really important, not being touched upon or 100% discussed. There may be threats to cause fear...instead of full acceptance. Come to think of it, if they're a bit more accepting, she might've taken responsiblity to show her appreciation of their love and acceptance, instead of rebelling like that.