If step mother is mentally abusing a 13 year old girl and the child does not want to go to the dads anymore what steps can the mother take..

In California you file a Request for Order to change child custody based on the abuse and in the process you can request a child evaluation.  In a child evaluation the 13-year old and you tell your story to the evaluator.  The evaluator will then reports her/his findings to the judge who ultimately makes the decision whether to change the custody arrangement.  Under California law, the 13-year old must be heard by the court in some method either testifying on the stand or talking with an evaluator.  Of course, in the meantime, you could take her to a psychiatrist or psychologist and seek a report on how that abusive conduct is hurting her.  You would include that report with your Request for Order Change of custody.  This could be very serious in view of the teenage suicide rate.  I had one teenage girl testifying on the stand, and when the judge asked her what she did at father's home, she replied:  "I call suicide prevention."  Good luck!