Try and get her interested in psychology or self-help.
Buy her a copy of a Norman Vincent Peale book.
Talk about the youth of today and how they need help in seeing a brighter future because young people, if they are patient, can really change the world. See if you can give her a goal.
Internally, only she can change her own mind. But a supportive environment that shows the possibilities to move forward can make a big difference.
Read up on the Socratic method and have some FRANK talks with the other members of your family about how a message is presented. If she will talk to her, and you can ask her questions, then there is a way forward.
I hope that you and all the other members of the family are also musicians. If not you need to learn NOW! Until you are a musician you will not be able to communicate with her.
People become musicians because they find that they can communicate in music in ways that they can't any other way. You have to step into her world view.
Everything you do has to be oblique. No head on confrontation. Make a vacuum that she falls into. Send a message right past her that she will notice as it goes by. Eventually you will make contact because she feels safe and secure, NOT ATTACKED, and wants to move on.