I had a wonderful relationship with my late MIL.
it was tricky at the start, I was 17 when her son also 17 and I started dating, she was definitely of the view that I was taking her son away and her last child to leave home etc. I never argued, was never rude to her, even though it was really difficult at the time. We bought a tiny flat at 18, and DH and I moved in together.
When we lost FIL, we really supported her through that horrible time. Then we got married. And years later had our children, who she absolutely idolised my sons could not have wished for a more fabulous GP.
Late MIL was the first person, I would turn to for advice. She viewed me as a daughter. We got on so well. When we lost her, I didn’t think I would ever stop crying. It was a totally awful time, accepting she had gone. She was absolutely great.
My children are adults now, and I can see how difficult it can be at times to be MIL. But I have always made gf very welcome in our home,I can’t make someone like me, that is for them to decide. But until you see the other side of the fence, I would save judging MIL so harshly.