I need some legal advise...please read more?

A fifteen year old has been sneaking out of her house to see her 16 year old bf, she already had sex with him and i have proof, the night i caught her she hit me and i have bruises. She's planning on running away and she's been discussing it on fb so i know all about it. Im a mother seeking support and advice. Shes out of control and her bf has criminal history so please anything that i can do will help. Thank u