What do you do with a 11yr. old girl that is boy crazy, sneeking on alot makeup, and dressing slutty?

My granddaughter is always talking and wanting a boyfriend. See sneeks on alot of makeup. Her mom throws it out and she sneeks hers. Her clothes are picked out by her mom but she rolls the top or puts on a belt to make them tight and short. Her mom and dad are very good people they don't know where she is getting this from. We are all very concerned what shall we do? Her grades are also failing. She is a very pretty girl. HELP!!