You cannot file any charges; you can only make a report (or report what you know to the prosecuting attorney). Given that you seemingly have a motive, it is unlikely they will accept charges on your complaint.
Was there ever a custody order done on the child? If so, she can enforce the Order to get the child back from him. She should talk with a good family law attorney to see what her options are. She should also have a good criminal attorney for the charges against her. Your attempting to file charges under the circumstances you outlined will not help. Tell her not to plead guilty. A finding of family violence will kill her changes at primary custody.
Have her call my office for a free consultation.