When that degree of harm exists with in-law relationships, and one retreats, it does become difficult to brave things out and to prove oneself as the absenting deepens the family rift and blame. Absenting oneself is limited protection. I know it’s hurtful. Even with my stepmother after my mother died. She just wanted to adopt the youngest two of my siblings, and the rest of us felt like second-class family. We weren’t good enough.

We braved it out for the family’s sake and for my Dad’s. It would have been helpful if she’d said sorry before she died for all the hurt she caused, sometimes, without witnesses, really quite cruel. I never answered, never caused a fuss, but in the end she did become more accepting and kind. In our case, braving out the discomfort and hurt, and being kind ourselves despite the fact we older ones couldn’t do right. That worked to keep the family united. So you see I do have some experience of feeling like rubbish for years. It hurt. I don’t know if it’s too late for you to ‘brave it out’, be only charitable back? Maybe this person, possibly your mother-in-law, is incapable of responding? But she has maternal fears, and there are issues, obviously that cause her fear, rightly or wrongly. That you don’t want act as part of the family, e.g. being present for family events, would exaserbate those fears.
Another relationship that was hurtful were my parents-in-law. We were 100 miles away from my siblings and father because my husband wanted to be near his parents.
They were of a restrictive kind of English immigrants. I was told off by his mother for not sitting square on to the table when I was 8 months pregnant and talking to her as she did something at the kitchen sink. I was told off for coming over to visit with my husband after my baby was born so I wouldn’t be left home by myself all the times in the week that he went to visit them in the evenings…and so on. So I do know that being pleasant yourself, and sticking it out can mean that eventually you are accepted and even welcomed.
In the first instance, I couldn’t and wouldn’t complain to my Dad who had enough on his plate. He never knew I left home because even everything I did to help, as I had helped my mother, was criticized. In the second instance, I couldn’t say much to my young husband about my hurt without getting my head blown off. He hadn’t really left home. That’s not easy. His mother did everything better than I did in his opinion, that hurt.
I guess I’m trying to demonstrate endurance and kindness from oneself can help to gradually change one’s relationship with in-laws, (and with stepmothers). I know it’s hard to live out, but the alternate is ongoing, exhausting warfare. I only once said something to my stepmother, when she said something hard about us older girls in later years. I explained a couple of things, and told her why I’d left home. Later, Dad said, that she had told him that she now believed that most of the problems with we older ones had been her fault. She never said so to us, but it was good to know at last that she saw us in a different way.
I hope you can find a way that these shattered and hurtful relationships, no less hurtful for her, no less oppressive, can be gradually worked out with kindness and positive approach.
I hope so, to end the maternal and family unhappiness that exists, and your own hurt and feeling of rejection.