Well, this definitely is a touchy situation. My advice would be to try and talk to her about why she is having sex. She may feel uncomfortable talking with you or her mom about this aspect of her private life, but being understanding will help. Perhaps she thinks she loves this person she is having sex with. Try to advise her of the dangers of sex, and why waiting until you are older is better. Ultimately, she will find a way to do what she wants. I would make sure she knows how to use condoms. I would also advise telling her to use another form of birth control. She is too young to go on the pill, so some other method must be used.