Unfortunately, your daughter is going to find a way to have sex no matter what your feelings are. You can simply continue to tell her that it is best to wait until a serious relationship..like marriage...and that many boys just "use" girls for sex. Also, you can try the scared straight approach and show of pictures of diseases that are prevalent amongst sexually active teens. This may change her attitude but she is at an age where she thinks she knows everything!!!! But Mom always knows BEST.
I hope that this has helped. Please ACCEPT.