We all learn from our parents how to handle these things, to whatever degree. If your parents have raised you in a cult where women are thought of as nothing more than brood mares, it warps your values. Maybe Anna has already seen this scenario in action, and learned that her place is to be quiet and supportive, and to turn her back to any abuse of her children.
It's essentially just a bunch of creeps passing around their daughters so everyone can have a piece. See the FLDS, watch Keep Sweet, Pray, and Obey. It takes a massive spine and inner strength to break out of this, and not to be completely shitty to Anna, but she seems very soft, mentally.