It's complicated, but it's simple...your husband is the one who has to fix this. He MUST stand up to his mother, kindly and with love but firm, each and every time. She has to know the boundaries and has to know that she absolutely cannot treat you disrespectfully and that if she does, he will side with you EACH AND EVERY TIME. (Of course, you have to give the respect back...)
I got sideways with my brother-in-law once and my husband supported me unconditionally. At first I got it from my mother and father in law, too, but the family eventually came around. When his brother was in my face, cussing me out, he defended me and told his brother to get out and stay out. It was close to a year later before my brother-in-law would even sit in the same room with me and they even skipped my birthday dinner completely! But when I stayed home from an event, so did my hubby and kids. When I got up to leave, so did my hubby and kids.
You have to let it be her problem and if the other women of the family gather around her and you are ostricized, then your WHOLE FAMILY (you, your husband and kids) skips the event...not just you. If just you stay home and he goes with the kids (or God forbid, just his kids), then your husband is sending the message that it's your problem and that he doesn't necessarily support your decision.
Without your husband's FULL, UNCONDITIONAL AND CONSISTENT support, this will never get better. She will only stop this when she sees that he supports you completely, that he will not let her interfere with his marriage or the raising of his kids, and that he will not tolerate her treating you badly.
Your husband is probably a sweet, kind man, and he probably needed and appreciated his mom's help when he was alone with his kids, and that makes it hard to stand up to his mom now. But he can't be torn on this issue. Unless he wants to be married to his mother instead of his wife, he needs to straighten his spine, thank his mother for her loving support, and tell her to BUTT OUT and treat his wife with the respect she deserves.
She'll eventually come around if she truly loves her son and grandchildren, which obviously she does. She is just threatened by being replaced.
Once things even out, find ways to include her ON YOUR TERMS. Let her help with something that will truly help you out and will also give her some time with the kids. She will still feel needed, which is where this whole thing started, and it will be on your terms, which will make it easier and more convenient for you and lets you live your life, be married and raise your kids with your husband as it should be.