AITA for not reminding my husband to call his mother for Mother's Day

My husband forgot to call his mom for mother's day. We don't really celebrate mother day. Mine died when I was a baby and my husband's mom kind of lives and breathes men. My husband was raised by his dad because his mom spent his whole childhood chasing men. So he's never really celebrated Mother's Day because she wasn't really around. His mom came back into his life back in January and they text every now and again. She sent both of us a very long hurt message about how my husband didn't wish her a happy Mother's Day but she was extremely upset that I didn't remind him and feels like I'm not being supportive enough of them rebuilding their relationship. My husband was off put by the message and left her on read. She's accusing me of purposely not supporting their relationship when in reality I don't care if he has a relationship with her or not. I knew it was Mother's Day but we have never celebrated it so no I didn't think to tell him to call his mom and tell her.