What can a 17 year old do when a parent is using fear tactics and psychological abuse to control for child support?

I am not sure where to put this, but here goes. 17 year old girl has been psychologically abused with fear tactics, by a parent and grandparent, to control the girl for her child support. Fear tactics includes threats to have girl committed as unstable mentally so that no one will believe anything the girl says. And also threats to have adult rights taken away. The girl has nowhere to turn. If she goes to authority figure the parent has threatened to have her 19 year old boyfriend put in jail for statutory even though there has never been intercourse. Her mother has said that it would not matter because a medical test would prove she has experience and they cannot prove it was not him. The truth has been covered by the parent for years because she does not want to be held responsible for the rape 3 years ago. The parent is telling her that she is lying when she knows she is not. What I need to know is what I can do to help this girl legally and what she can do to get away without any repercussions. The girl would not go to the police in fear of what will be said about her boyfriend. Can she just leave without a parents’ permission since she is 17.