As for myself, I never had a mother-in-law, she was nefter when my husband was younger.
My husband, though addresses my mother as Ma. While my sister-in-law, refuses to call my mother her, mother in law, Mommy, Ima, Ma… because she feels that she only has one mother and can not call another person by that title, even though, my mother would like it. Let’s just say for shalom bayis, we gave up trying to convince her. Now that she has children, she calls her grandma.