Why do i always avoid my mother in law??

She sees the positive in everything for example when im feeling really down, my mother is telling me to drop dead and go kill myself and im in bits, she'll sit there with a big smirk and say shit like "im sure your mummy tries her best". No hug or comfort or sensitivity. She defends everyone else against me and her son, tells us what to do and what we shouldnt do. And we arent allowed to move out of the neighbourhood because she "needs her son around". Shes 55 not 90 and her son drives. Not like we see her much around here anyway and we'd be moving 5 minutes away. Shes really awkward and can be very twofaced. Im still tryna figure her out and at the same time try so hard to get along with her. Its hard to string up a sentence when i feel i cant be myself. She has a real strong influence on her son and everyone for that matter as she plays a huge part in the community and is a public speaker. My SO is now noticing i avoid her as much as i possibly can! How can i fix this? Being around her gives me serious anxiety.