Be sure she has your emergency contact info in her wallet and phone.
Before she returns to dad's, help her identify people she can go to for assistance should she feel she must leave dad's house. Talk to her about mandated reporters and what they can do to help her. Explain how to go to the ER if she needs emergency medical care, how to call police and CPS , etc. She is old enough that she should be able to solve problems with dad without having to go through him to get help if things are really bad. Let her know that there are safe places if her home is not.
I am confused about her school. If she is in public school, there should be a counselor or social worker to help her.
Her knowing what she can do will give her the confidence to go back until you can deal with the legal issues.