parenting the sexualy abused child.

I thought that when my daughter was 13 things were bad because I had to constantly check her bag so that she wouldn't change clothes on her way to school. (Very provocative) Then I thought that 16 was the worst when I kept catching her bringing unknown boys into our home to have sex. But I think now that she is 18 (she still has one year left of high school) it has gotten so bad that I can't imagine what could be worst. She says that she is going to go out with a 22 year old who has his own place and that there's nothing I can do about it. When I try and tell her that she should be cautious and or NO, she gives the ultimatum of she will just move out. Which I am tempted to let her do except for the fact that she would just destroy any opportunity that she is ever going to have in life. I have tried so many things to help her over the years since I took custody of her. Love first and foremost, but also discipline, support, and a consistent amount of therapy and parental attention. But it has all failed miserably for her, which means I have failed her miserably. I pray that things don't get worse for her, but I know that it will since just like her mother she will have to get to rock bottom before she opens her eyes.