Worried my husband may start talking to my MIL again

My mother in law has always been extremely shitty towards me. She had went around and told everyone in the family that I'm a hoe. She intentionally spilled wine on my wedding dress. Has told me to my face when me and my husband were going through fertility issues that a woman who can't give a man a child is a worthless woman. Has called me a bitch. Threaten to hit me when she got drunk. When DID get pregnant, told me she hoped I lost the baby and then I did. She's been AWFUL to me. We haven't spoken to my MIL in 4 years. My husband has had his own issues with his mom from childhood because she convinced his therapist that he's a liar and he's the problem so his therapist would believe his mom and not him.

Well like I said it's been 4 year and me and my husband were just watching TV and out of the blue he gets a message request from his mom's new Facebook. She sent him a picture of a book called adult children of emotionally immature parents. She said she saw this book at a garage sell for free and something told her to get it and that she has read it 3x and realized she did a lot of the stuff in this book to him and she understands if they can't have a relationship but she wanted to say she's sorry.

My husband got a little emotional reading that and has been typing a reply but keeps deleting it. My issue is nowhere in that text did she mention being sorry to ME for what she also put me through. I don't want to deal with this woman anymore. I know she's his mom but I always believe the wife comes first. Especially when your mom treated your wife like trash. I don't want her back.