She doesn't sound very repentent.

Your husband should say to her, "Mother, do not criticise my wife when we visit, or we will leave immediately." This lady needs real simple ground rules.

My father was like your MIL. He used to want to talk bad to my sisters and me about our men, and to our men. We adopted a zero tolerance policy. He was reduced to sulking at family get togethers. Then our mother told him to knock that off. It more or less worked.