My sister has lost emotion for my father and she is paranoid about him as if he is a threat to her and really hates him.what should we do to fix that?

Defining the cause: How old is your sister? If she is an adolescent, it may be related to a normal developmental period of reevaluating your parents and her relationships. Does your sister have a legitimate reason to fear your father? Is he overbearing or abusive in any way that would contribute to her fear? It is important to get to the cause of her emotions in order to design an effective treatment.