MIL called me a cunt

Me and my husband have been together for 12 years. We've been through a lot because he's struggled with depression, alcoholism, and suicidal thoughts/attempts. He lived with different family members and foster homes in a majority of his childhood and has opened up to me about a lot from his childhood. It recently came out that his uncle (mom's brother) was sexually abusing his step daughter. It wasn't a surprise because he did the same thing to my husband when my husband lived with them. His mom found out it happened to him too and found out I'm the only one who knew. She thinks I told him not to tell her which I didn't. He even told her him not telling her was his own decision, not mine. So she thinks I'm trying to come between them. She even called me a cunt in front of others because she's mad at me over me knowing this about my husband. She refuses to believe I had nothing to do with him not telling her and believes I had to have told him not to because a boy should tell his mama everything. I don't know what to do to get her to stop being mad at me. I didn't even do anything.