The saying "She's no better than she should be", is taken as a negative comment, but actually the words mean that someone is acting as they should. So where does it scome from and what does it really mean?
This was traditionally used to describe women of a dubious morality, and was first used in the early 17th century. It's not clear why it means the opposite of what it actually says, but it's used euphemistically, so maybe no-one wanted to be seen as pointing the gossipy finger by saying something more obvious.