What am I supposed to do with mother-in-law hell?

Okay, just hang in there. You don't have much longer to go, hopefully, even though it will feel like an eternity. I like your strategy of being courteous and respectful. I know it will be extremely hard, but "kill her with kindness," and she will have a harder time being rude to you. Just continue being respectful and courteous to her and go out of your way being "kind" to her. She may actually come to like you eventually. Give it a try. What can it hurt? Best of luck, because believe me, I know how mother-in-laws can be.