How to get respect from your in laws?

My mother in law has always been really mean to me she used to pet my head like I was a dog and I told her how she made me feel she went off on me and said oh im so sorry i offended you in a snobbish way. She has accused me of sleeping with her ex husband and I finally had enough and said I wouldnt sleep with anything that has slept with you! My 3 children have always been treated differently then her other 3 grandkids. If I buy a vehicle she buys one just like it just a different color. I have never talked about her behind her back or said anything rude to her other than the time I had just had too much with her accusations. Once she drove 7hrs to borrow $10,000 from us why our daughter was in the hospital recovering froma major surgery and turned around and left an hour later, we told her the money had to be paid back in a couple weeks bc of bills that were due and she agreed and then turned around and we had to call her for 6 months in order to get the money, and to her I'm horrible