Manipulative relatives

My husbands brother's widow is constantly trying to Get me to chauffeur her around so she can feel like she has a servant. She is extremely rude and demanding, critical and did I mention. cheap? She has plenty of money but has never had to work - recently she had surgery and needed help so I stepped up. She has no one because she is such a bi--- to everyone. Her behavior toward me was thAt of an angry mistress towed her slow stupid maid. Every conversation or encounter ends up with her mad at me for some slight thing I did not do to her satisfaction. Finally she was well so I stopped calling and I felt FrEE. Now she is getting her friends to call me and ask me over so that I can't politely say no. I've told her friends why I don't want to come but they say they'll be hurt if I don't come. I resent her trying to manipulate me this wAy and just wish she would leave me alone! I can't tell her to bugger off because of the family; but soon I have to deal with the friend and tell her I just want nothing to do with the sister in law! I just need the words , tell Nadine I am not interested and leave it at that? I don't want to appear ride but I cannot stand her any More! I sm too old for john school games !