It's hard to see your MIL act out, especially if it's behind your husband's back. When this wife is conflicted, she asks Reddit:
My mom had a birthday recently and had a girls night. She wanted to invite my MIL, because they are becoming friends. I was really uncomfortable as MIL and I do not get along at all. It is bad enough my husband has had to go low contact, but my mom guilted me into inviting her.
We were at a fancy art studio with various lessons and wine and charcuterie boards, and MIL refused to wear her top (relevant later) so she had top that might have been a bra (I couldn't tell) and got resin all over her stomach. MIL freaked out and my mom went with her to try and help her wash it off (wtf)
I went into the bathroom as I wanted to wash my hands and overheard them talking
mom- your stomach is so flat. I hate you