I would recommend you seek the advice of an attorney. If she comes back after being physically assaulted (marks or brusies) or is in fear of her personal safety to such as an extent that suffers substantial emotional distress, you may be entitled to take out a domestic violence protective order in your state on behalf of your daughter, depending upon your laws.
An attorney can tell you the age that would be appropriate for your daughter to be able to testify, and other important considerations.
Based upon your information, you may also seek to file a motion to modify custody in NC.
Again, there are several considerations so an attorney can help you figure out the best course of action in your state or in NC.
I agree with Mary, and would add that if you feel that the situation is extremely bad, you might want to contact Child Protective Services as well as taking out the domestic violence protective order
Sign up to receive a 3-part series of useful information and advice about child custody law.