D.T.
I'm no expert but haveing been told that she doesn't exist by her father may be the key to it. Her main male authority figure just broke her heart. I would have been devistated if my father had said something like that to me at 15. More evidence of this is her respect for the new boyfriend, she needs a male role model. You can suggest the two of them, mom and boyfriend talking to the girl or even just boyfriend. I think she might open up to him. I hope this helps.