I'm with EKGO! My parents let me go to stuff like this when I was that age, they trusted that they had brought me up with enough sense not too get into anything too dodgy! I'm not saying I was an angel, but they always knew where I was and came to pick me up. I never came home drunk (I saved that until I was in my 20s!).
If you trust her to be sensible, set out the ground rules and make it clear that if she doesn't stick to them it's game over for her social life!