He can't stick his head in the sand. There is no shame to her. His attitude about it is medieval and poisonous.
This is about her mental health..as well as your own- as well as his responsibility as a parent. Of course, he's dealing with his own grief but where has he been when the abuse happened? Was the abuser caught?
Where is his caring for her now? If he is dealing with guilt over the abuse...but then punishing her ... that is criminal. She's innocent and he's ignorant.
She needs counseling. If he ignores it, it'd be like tossing her to the wolves. He most likely need counseling, too. The responsibility is his. If he ignores it...it makes matters much worse. you can';t make up for his ignorance. No matter what, he has to be involved in her healing. you can help somewhat..but he's the responsible parent and adult..whether or not he takes the reins.
Can a relative or friend of the family ..some close relative or member of the church/temple..or community help bring this across to him?
I'll ask again...how old are you?