First of all you are to be commended for taking in your sister and caring enough about your family to want to get some help for the problem. Good for you. Secondly, since i don't know your family personally I can only go by what you have explained here, but maybe your dad is going through something that he hasn't told anyone about. Also, since it is his step daughter he could be experiencing grief over other problems concerning children or young females in his life. Maybe he is suffering from some kind of loss in his life and he is taking it out on her. Like you said, psychotherapy treatment would definitely get him to get to the root of his problem(s) and move through them. But on your part it would be commendable to keep loving him and being supportive of him no matter how his days may be.


