Protect your child AT ALL COSTS!

My mom never protected my brother from my grandfather's BS. (Well, she never protected any of us kids, but my brother took it the worst.) he ended up having panic attacks and meltdowns.

Screw your mother in law. She's an adult who has chosen to behave badly. Your responsibility is to your child. If bridges are to be mended, she needs to extend the proverbial olive branch ON HER OWN, not because someone else has stepped in to "make things right".