It must have really caught her with shocked and been difficult for her to actually resist, I understand the position she was into. I believe the mother was just been bothered about the behaviour of his wife and the state mentally that will affect the daughter. But it seems the man was not seeing it from that angle and decided to just push all the responsibility which his wife should carry out upon his mother head. That's bad for him to do though, well thank God he has an understanding mother also because that really matters.
As the story flow, I begin to realise the wife might not really be naughty as the mother claim, probably the mother didn't love the wife and also the children from the wife and so resulted to that much hatred and dislike for her. This happens in some homes where mother's have issues with the wife of their son.