It depends what kind of relationship we have. Generally speaking, I would tend to limit interaction with them.
Islamically speaking, what she’s doing is quite wrong. Adultery is a major sin. I can understand the parents being upset about it though I don’t say that it justifies abuse. As janab-e-ali said, people speak ill of others for less than that.
I can’t say that she’s no longer Muslim for it, but I can understand people cutting off relationships over it.