Butterfly4

My 4 yr old step daughter hits herself in the face and yells " I hate myself" when she is in trouble. Her father and I are worried about her and don't understand why she reacts like that. When we ask her about it she justs says because she does. We believe it might have something to do with her home situation. We only have her on the weekends and her mother says that its a normal thing with her. We are at a loss of what to do and would appreciate any advise on why and how to help her. Thank You