I have a question about my mother

I am 37 years old. I don't really have a good relationship with my mother because she is controlling and emotionally abusive. I have a half brother that I don't really have a relationship with either. I left home when I was 19 because my step-father "asked me" to leave. My mom favors him over me.
Ok, so my brother just turned 21. I sent him a card. I never talk to him on the phone. My mom reminded me of his birthday which was last month. Now she keeps telling me to call him.(through email) I don't want to call him because I really don't know what to say to him. I don't know why she expects me to call him. He never calls me for my birthday or sends me a card. Not that I expect that but why I am expected to do all this for him when she doesn't expect him to do the same for me? I had major surgery about 3 months ago. My mom was so mean to me and really stressing me out. She didn't tell my brother to call me after my surgery. Plus at 37 years old should she even be telling me to call people?????
I don't even feel like this is about my brother. I feel like it's another attempt of hers to control me. If I don't do this she's going to guilt trip me.