OP I have so much sympathy because I've been where you are .. as far as the constant criticism anyway. Thank God though she lived at a distance and we only saw her every month or so. More than enough.
It's easy for people to tell you to stand up for yourself and stop putting up with it, but if she's aggressive by nature and you're much nicer, it just seems very daunting. My MIL had a lot to say and if challenged on any of her opinions would get quite angry and as I'd had a dad who, although loving, had a short temper and I had a deep-seated instinct to avoid conflict I think.
My problem was that I started going out with DH when we were teenagers and I didn't have the life experience or confidence to know how to handle her. I was never good enough for the apple of her eye and I won't list all the ways she criticised me as it's boring but basically my house was never clean enough (it was fine) she didn't think I dressed glamorously enough (I was a mum of three little kids in my twenties and wore jeans a lot) she didn't like my cooking (honestly it was so much better than hers just a bit "foreign" and with al dente vegetables etc) and on and on and on. The most hurtful comments were when she criticised my parenting though. That really stung.
DH didn't stand up for me either and that was a real problem. I still feel more than cross about it. His attitude was "it's just what my mum's like" and wanted me to take no notice. The constant carping can really get you down though.
Eventually I'd had enough. The day my dad died and I phoned to tell her her reaction was all about how shocked she was, how upset she was; very over the top and dramatic. All about her which was typical. I remember thinking "This is MY dad! Your reaction is so selfish" And something to do with the loss too; something so serious had happened and I suddenly didn't feel scared of her getting cross with me any more if I stood up for myself.
We never had a huge falling out. I just calmly challenged her from then on when she was being ridiculous. And I would point out when she was being rude or hurtful. Once she almost even apologised. Unheard of! And just like @Knotaknitter above, it was amazing how she managed to tone it down. In her old age she even started to compliment me sometimes. In reality she was a bully who needed to be stood up to. I wish I had done it long ago.
I think if you can be brave and calmly challenge her, you might surprise yourself OP. It's not easy but it can be done. Good luck.