Oh, hugs to you sweetie. I would not know what to do in your situation either. I totally don't know why your friend did that unless she is too scared to reveal what happened to her and she is hoping that through your actions with the police that justice will be served? I don't know though, I am just reading what you posted and really just want you to feel better...but I know nothing I say will do that, I am sure you feel betrayed, I know I would.
Reliving it all is the worst, and you thought you had an ally and now she is denying it. I am sorry. Is there any way you might be able to tell her how her quick turnaround on her experience with the abuse has affected you and now you feel alone? I don't know if that would even help, but it's a thought.
I am not used to giving advice, or sharing my thoughts, I am afraid I may be way off base here, and if I am please forgive me I Hope you find what you need, and I hope that you continue on, you are strong to have gotten this far... HUGS to you