Can A student (age 17) transfer schools without parental permission

Hi, I am hoping someone out there can help me or guide me into the right direction. My boyfriends daughter is 17 (will be 18 in two months) and wishes to to transfer back to her old school to graduate with her friends. She is an excellent student, she only has to attend two classes and will officially graduate (in January) earlier than her other peers. She has moved in with her boyfriends dad, so she does have a legitimate address. The problem is that her mother originally agreed to enroll her in school, but is now procrastinating on following through. Is there any way that she can enroll herself in school without the authorization of a parent or court ordered legal guardian. Her father is behind on child support; her mother says that he he is not allowed to see her. I have not seen any official documents to prove that this is true. He is scared of what problems this may present with local authorities if he enrolls her in school. We do take care of her financially by sending her money directly. Her mother is very unreliable, because of issues I would rather not discuss. It's been almost two weeks since she has left her other school, I am afraid that this may jeopardize her chance of graduating early, or at all. Considering the conditions she grew up in, I am in awe that she has accomplished so much. Her mother is angry because she found out that her father went to visit her, so she is retaliating by not enrolling her in school. Someone...Please help me to figure out a way to get this child back into school.

P.S.
She is transferring from Houston, TX to Atlanta, TX