Probably something sad like a delusion of "we have to make it work for the children" or she might not be in a financial position to leave him. I'm always stunned by the reddit stories that go "Well, I found out they were cheating, so I bought a new house three states away and moved overnight."

This is a good question. Probably a combo of: - divorce is taboo in her own family - she doesn’t have her own financial resources - childcare seems too overwhelming (too young, too many, or special needs) - she blames herself and doesn’t realize how abusive the situation is