AITAH for defending my mom and not feeling that she was rude to my wife?

My wife and I recently had dinner with my mom and her husband. For some context about my mom her face never moves, voice never changes, never laughs, smiles, gets angry. The only person she has genuine emotional reactions to is her husband. With everyone else is is 100% stoicism. Understandably my wife feel uncomfortable and they have never had a good relationship.

My wife had an embarrassing moment at dinner and accidently farted. It was loud, really really loud, and my wife immediately went scarlet and my mom stayed in character and did absolutely nothing. She did glance up when it happened, but then just went back to eating. I quickly changed the conversation and tried to distract everyone, but my wife was bright bright red.

After dinner, when we were alone, she blew up that my mom sucks and any normal woman would have tried to make light of it and make her feel comfortable. I pointed out that my mom never reacts to anything, and she shouldn't have unrealistic expectations of her. My wife said I was just defending her and a decent mom or MIL would make a joke, say something self deprecating, anything to make her feel comfortable. I tried to point out that when has my mom ever laughed or joked with her and it would have been so out of character, but my wife didn't want to hear it. She blew up that I don't know how humiliating it was as my mom is always so perfect and put together, and that I don't understand because I'm not a woman.

I just feel expecting my mom to become a completely different person is unrealistic.