Can she cook? Mine is a little crazy, but she's nice and is an awesome cook. Every time she visits, it's like living in a lebanese restaurant. kanefi, shish taouk, lebneh, shawarma, olives, and fresh pita ALL OVER THE PLACE! AND DON'T GET ME STARTED ON THE MANA-ISH (<--maybe I should move to pizza thread?)
But seriously. Be nice to your mother-in-law. Your wife will eff you for it.