I feel like my Mother In Law Hates me!

I don't know if I can take much more. My husband and I are very happy. We have been on and off since high school 16 years and now married for 3. We live on a big farm with his parents and have since we got married. Reason being my husband started a new business and I went back to school. We are gonna be building a house or buying one soon, but a lot of why we live with them as well is his parents are a lot older and can't do much. His dad's health isn't very good and now his mother is having heart problems and really can't do anything at all anymore. She used to be pretty active. But my husband and I literally take care of everything around here. But before she got sick in the last two months, she always makes rude comments to me or just flat out is mean. I was raised to respect your elders especially my in laws. It came to a head and my husband and I had it out about it before she got sick, he never noticed how she treated me until we had the fight. Now he started noticing. Well since she has gotten sick it's gotten 10 times worse. I'm working all day and then come home clean, take care of them, cook dinners, do anything and everything I can to help and release the stress from her and them, but my patience is just gone. She is just so rude to me and doesn't appreciate anything. Last Sunday I cleaned the entire house from top to bottom then made a fancy dinner, and while I was cleaning she flat out told me I will just have to clean around her cuz she wasn't moving. I normally don't say anything because she has already told me I can never disrespect her or my father in law. So I just shut up and do what I do but they  can tell I'm pissed and I snap. I don't know what to do anymore. My husbands company has become very successful the last few years and he has gone out and bought trucks trailers and both his parents get so excited and brag about it. Well yesterday he surprised me and bought me a Tahoe, and I have told him over and over I didn't need a new car, even though I really did. It snows here and he wanted me in something safer with 4 wheel drive. Anyways she is pissed he bought me the car but taking it out on me. I overheard he this morning talking to her daughter saying I don't pull my weight money wise and is pissed he bought that for me. I never ask for anything and I work all the time, but don't make nearly what my husband does. I started crying and told my husband I didn't want it anymore. I feel like I can't even enjoy my new car. She is making me feel so guilty. I had told him what she had said and he is pissed but says we need to just let it go for now and we can afford it.  She is in risk of a heart attack or stoke so we can't say much right now. And have to keep all the stress off her.  He said you deserve it and we can afford it and you need it. I just feel overloaded and feel like she just hates me. If any of her other kids got a new car she would over the moon about it. But since he bought me a car she is pissed. Sorry for the long vent session. I just don't know what to do anymore. My husband says we're all gonna sit down and talk soon. And he got in a fight with her yesterday about me and told her how she has been treating me, but she still acted the same way the same night and even the next day. Am I over reacting or what? I feel like I'm gonna snap. I don't want her to ruin my marriage but I feel like she is. I can never do anything right in her eyes. Help!?!?