If you think that endangering your family somehow makes you more holy, thts your prerogative.
I simply think it wasn't a wise course of action - the better course would be to not bring the guy into the home. As it was, this girl paid a heavy price for her mother's lack of prudence, and should be thankful it wasn't much, much worse. Even so, this was a life altering thing for her.
Consider it a learning experience for us all.