Check with the parents to be sure they will be supervising. If any of the parents of your daughters friends, know the parents where the sleep over is held, don't be afraid to ask them about the parents of the host girl. Also ask about the girls dates, if they will be there and what time they will be going home. If you get satisfactory response from the parents, and if it is a girls only sleep over, let her go. Of course she would get the "we trust you to use your head talk--grin". When my daughter was that age we had this come up. After talking with the other girls parents we were satisfied it would be a girls only and it would be supervised. Never be afraid to check, then give your daughter a hug and tell her you love her and trust her, but sometimes bad things can happen to good people.