@Harryyourenogoodalone I'm so sorry your daughter is going through this, and your husband is not supportive.
A personal anecdote for you:
My grandmother was not a nice person. She treated my dad like literal shit, and then when he got with my mum, she treated her like shit too. But when my parents broke up, my mum still made the effort to travel to see her, and sent her cards and gifts even though she was just horrible to her. Direct insults about how fat and ugly she was, and sorry she wasn't very successful either. That sort of shit.
She started to transfer that onto me as well. I graduated uni, bought a house, had TWIN baby boys....but I was fat. So worthless. And my poor boys - no one wants boys, they all want girls you know
. Oh, and at my wedding? How beautiful my sister looked.
Anyway, about ten years ago my mum abruptly stopped engaging with her. It took my paternal grandmother making a nasty comment about my maternal grandmother (who'd died over 20 years before) for my mum to allow herself to set herself free. I'd been saying it for years - she owed her nothing.
I only saw her when I absolutely had to in group settings, and I have never felt guilty for that. I don't owe someone who is mean to me, any attention at all. And neither does your daughter. Shame on your husband for saying she should just grin and bear it when MIL is mean to her!
TL;DR: Your daughter doesn't owe your MIL anything at all. And your husband should be ashamed of himself.