Mother in law drama- need advice

I have been married to my husband for 4 years and I have a great relationship with his parents. When we had a baby boy, his mom has never respected our boundaries as parents. When we would say don’t come over right now, it’s not a good time, they would show up anyways. Never listening to us. Always putting her 2 cents when it’s not needed. When he was just trying solids, we asked her only certain foods he can have, well I walked away and came back and found out she’s shoving food in his mouth that we clearly said no too. Telling her to give him a pacifier if he cries and she would rip it out of his mouth and say, I don’t care if he cries.
She doesn’t care what we have to say. We created some distance from her and only see her in certain situations. I have made my husband say stuff to her but it causes a huge fight with her and her always being the victim. My husband has learned to just deal with her BS because she’s been like this and he has learned just to take it. He’s annoyed with her too.
Well fast forward to just recently, we asked her watch him. He’s now 2 years old. She had to watch him for 3 hours. We went over the rules and we laid him down for a nap. Well I did confirm after we left, he was sleeping because I have a phone app/camera. Well she went in and woke him up and when we called her, she made up lies saying “he had to go potty” , hes not even potty trained. She ended up keeping him up and ignoring us and the rules we told her. We talked with her through text message and she said “I don’t regret nothing I did” and saying “I know I’m fired”. I’m just furious at this point because she has never respected us and has walked all over us. Just to think she was planning on never following our rules for our son and went behind our backs. She’s acting like nothing is wrong. I’m at my breaking point.
I’m about to message her saying all of this and telling her she needs to respect us and that I need a break from her. She is a narcissist and has never been held accountable for her actions. There is so much more to this than what I’m writing. My husband doesn’t like causing conflict so that’s why I planned to send her a long detailed message. I just need help. Like am I crazy? Is even messaging her and telling her all of this make a difference ???