I'm adding "nontroversy" to my personal lexicon, so thanks for that!
I'm so sorry you're having to deal with this immature, tantrum-thrower of a mother-in-law. In my family, the fit-pitching child in an adult's body is my grandmother. And, I'm still left reeling every time I talk to her, so I don't know if I'm the best person to offer advice. THAT SAID, there is a great post on Captain Awkward about a difficult MIL named "Alice", and the advice is great. Even the comment section is great. I think you might like it.
One concrete thing I would advise is to stop expecting MIL to behave like a reasonable person. She never will. We JADE because we expect to be heard and understood, but she never will see reality. Her mind is too warped. There are really only two things you can do! You can try to learn techniques to mitigate some of her fit-pitching, and to lower the stress you feel when she does pitch fits (and she always will. I'm telling you, if she has the energy to pitch a fit on her deathbed, she will. My grandmother was still throwing nasty barbs as she was going through healing from a double mastectomy and cancer treatment, and she was throwing them to the people who gathered around her to support her!). Some of those things include learning not to JADE, a technique called "medium chill" (this one worked for me for years), Structured Contact, Low Contact, etc. The other option is to go No Contact, which I don't think your husband is willing to do just yet.
One thing that I don't think will help the relationship is telling her how you really feel. Now, it might be cathartic for you, but there is no Come to Jesus moment with a narcissist. They don't get "lightbulb moments" or "moments of clarity" like the rest of us do. To have a moment like that, you have to be able to see yourself and others as separate entities, you have to understand that you are capable of failure and have foibles, and you have to be willing to change. A toxic person like you mother-in-law can't do that. She doesn't have the ability. It isn't just that she doesn't want to. Now, she will parrot sentiments that will make you think she can/wants to ("Let's work this out!" "I can't stand this hurt between us!" "But faaaamily!" and so on.) Saying these things in the past has gotten people back in her sphere and being nice to her, in the past, so she tries it again.
The only reaction she will have to you airing your (COMPLETELY REASONABLE, UNDERSTANDABLE AND JUSTIFIED!!!!) grievances will be to rage, and then go pathetic ("Why is she so meeeeeaaaan to meeeee?!?!") It might make you feel better in the moment, but it won't get you what you really want, which is for her to see the error of her ways. There is NO getting to that outcome, though, and I, an internet stranger, give you permission to stop pouring your emotional energy down this particularly nasty black hole.
I wrote you a book here, sheesh. Haha, your terrible mother-in-law got under my skin, too! :D :D
I wish you all the luck!