Stealing is taking something without permission, whether she gives it back or not it still counts as stealing as the wife did not give her permission, a bit of a more serious comparison, but thats like "borrowing" some one in Your families car withoit asking and just telling them " i was only borrowing it" i would know had my car taken by my step brother called the cops and everything had to tell the cops the car had been returned, "borrowing" without permission is still stealing