Mean mother in law

My mother in law is a negative mean old hag and has been my whole married life.. 30 years.
I have married grown kids that she pecs at as well. (They are always doing something wrong in her eyes) I under stand “the manual”and know I had a very thick one of how I thought she should be.
I can let it go…. because I realize she will never be the way I think she should be.
My problem is… i don’t think she deserves me (my love/kindness)
I can think different/better thoughts of why this or that and give her the benefit of the doubt,
But when I try to like her or move past all of it I feel like she doesn’t deserve it, and it feels fake for me when I try…
For me it’s easier to avoid her and not have anything to do with her. ( I was calling that “boundaries”.)
But my husband wants me to try. This is probably the one and only thing we fight about.
I show up ugly and like a mute when he makes me go to family parties because I can’t forgive her I guess…
I feel like she deserves nothing from me.

How do I fix this?