Astrologically, why does my sister hate my dad so much?

She is a Cancer and he is Aries. Aries and Cancer don't go well together but as father - daughter relationship astrology can't be a matter. You should not look at astrology when it come to family. You can't change zodiac signs of your sister and your father. Usually Cancers like their family members a lot doesn't matter what their signs are. If your sister doesn't like her own father that means that she has some mental problems. If she hates her own father who never did anything to her then it is not normal.