Long weekend

Time to update you all on the drama that surrounds PITA. Again let me state for like the one hundred millionth time....I love this child with all of my heart and soul, but I am just about ready to kill her.
PITA got a myspace. I told her it would be fine, but there was one little rule....I had to have access to her passwords so I could check up on her when need be. She has given up fighting this rule since her time on the internet is few and far between. She feels better giving in and having sometime online, then fighting and never being on the net. So this weekend she went to be with my little sisters. My stepmom picked her up on Friday. Hubs asked me to change her password on her myspace that night. I told him no, and I am happy that I didn't. PITA is one of those kids that if you give her just a little bit of rope, she finds a way to creat a noose, wrap it around her neck and jump from a box. She did this quite well with her myspace account this weekend.
Last night while reading her messages (not the public ones) I found she was having a rather explicit conversations with two young men. One of these gentlemen was nice enough to send his phone number so PITA could call him. Being the very involved mother that I am, I called this number to find out why an 18 year old boy was talking to my 15 year old daughter about things she could do for him orally!! Ok, so I was a little angry and didn't give him a lot of time to talk and in my anger I hung up on him. He called back and tried to explain one more time to myself and hubs that he did NOT write those messages, but would get to the bottom of who was using his account. After we got PITA home (she was picked up by hubs and our neighbor at 11pm) and a lot of yelling on my part and crying on her part, the house retired to bed around 1am.
This morning while on our 2 mile walk, my phone rings. It is the boy's number I called last night. However it is his dad calling me. He assures me his son didn't send the messages and apologizes again for the messages being sent to my daughter. He tells me what a good son he has and how he is a leader in his church. Funny thing is, when I go to this kid's myspace and check him out, he is with a teacher I respect VERY much in our district and his dad is a man I have listened to at the Texas Counsel for Social Studies for a book he wrote base on some letters he found of a distant relative from the Civil War and is also a VERY respected teacher in the district. I would have LOVED for my daughter to have this boy as a friend because he is around people that are a great influence. And guess what, PITA was the one starting most of the conversations that her and these boys got into about sex.
Here is my question now to the world out there....or my two readers.....how do I punish her? Grounding isn't working. Having to be in summer school because she failed is a joke to her, she is just happy to be with friends again. She shows no shame for her behavior that is COMPLETELY inappropriate for a girl her age. What is a parent to do?? Everyone tells me I am doing everything I can. I have made all the right moves, I am involved and she will get it sooner or later. But what on earth is a parent to do until they do get it????? I am sick, seriously SICK about what she is doing. I know I can't let her go to her grandparents' homes anymore because there is no one there to supervise the kids. They can run around and do whatever they want. Heck PITA had a boy meet her this weekend at my stepmom's house. I am trying, but I feel like I am fighting a battle I can't win.

thank you for letting me rant......peace out my peeps.....I hope you all have model children that every parent hopes for and that your biggest issue is that the child won't eat their veggies.