Gosh, I couldn't imagine. My MIL lives 700 miles away and is rarely here to visit. When she does come, she doesn't say anything about my house keeping or lack there of. I have kept her wild child son on the straight and narrow for over 20 years. For this she and FIL are eternally grateful.
To the lady who's MIL refers to you as her sons "First Wife" The next time she drops that little bomb look her right in the eye and call her "Your first MIL", then very sweetly say "Maybe I'll do better the next time around."