I agree that the stepmom should have left the "challenged" child at home and was probably using him as a tool for sympathy. I also agree about not calling the new wife mom. Mom is a name that we reserve for the one who participated in our upbringing. Obviously, an adult child is going to get very little upbringing from the dad's new wife.

I didn't say anything about her not having the right to reject the new wife. I said the new wife is the wrong one to be trying to change the situation.

The father does need to have the talk with her. If it comes down to an ultimatum, the father is the one that should be making it. She will always be his daughter, but he made vows to his wife and should stand up for her. If the daughter chooses her anger and resentment over a relationship with her father, that is her right.