Toxic Mother in Law

I’ve been with my husband almost 8yrs, and we’ve been married for 4 of them. My mother in law has never liked me, despite saying she does her actions have always said otherwise. We now have 2 children, and recently I called her out on something she did. I’ve been having issues in my marriage whilst pregnant with my second child. When my mother told her what had happened whilst I was pregnant, she justified it and never said it was wrong or inappropriate. I’ve now called her out on it, as her mother in law shared a not so funny meme to my husbands Facebook, which insinuated that he should buy himself something for valentines and nothing for me. My MiL basically laughed at it, and did nothing to tell her mother in law that our marriage is sensitive and it’s a poor joke. My MiL has now taken the part of victim, and changing the story to talking about her past experiences with her ex-husband (my husband’s dad, who is now deceased). And denied she ever condoned my husband’s behaviour whilst I was pregnant, despite me and my mother both hearing her. I’ve received no apology, and in the past she’s always quite passive aggressive towards me. (For obvious reasons I’m not sharing what happened, for context my husband wasn’t being faithful) Best way to deal with this? As it could effectively ruin my marriage