Most learn by mistake so maybe she learned her lesson. I would tell her they are not use to being outside AT ALL and they MUST stay inside or she will just have to go find some somewhere else... Then relay some horriable stories of what can happen to them outside... Annoy a neighbor and get shot, kicked or fed anti freeze..Road kill, stolen to be abused and abused for fun.. Paint her a true and accurate picture of what all happens out there in the world now.. Not to mention the diseases it can get in cat fights..