Narcissistic Mom

My mom completely cut me off 6 months ago. She blocked me on everything and hasnt talked to me since. She still visits my younger brother every other week though. Two years ago, her and my dad got divorced and I got so fed up with her lying so I decided I wanted to live with my dad and the judge accepted that. He allowed me to live with my dad, and my brother to live with my mom. After I moved in with him though, my mom did everything to make my life miserable. She wouldnt take me to my school events, told me I wasnt allowed to take certain classes (my show choir class), and even made me quit cheer. We argued constantly because she always made it obvious she only cared about my brother and always talked bad about my dad and I. She didnt even tell me happy birthday last year, her boyfriend did, she just walked past me. The last time I saw her, we werent arguing, we hardly talked. But of course my brother still talks about her all the time which bugs me, but I let him talk about her because I don't want to be a jerk. About 2 weeks ago, she sent me a letter in the mail saying she forgave me and that she wished me the best in life and I'm not sure what to make out of it, I dont really have anything to be sorry for, and I don't know how to or if I should respond. I dont even know why she stopped visiting me still. She mentally abused me for two years but she forgives me? I'm not sure what to make out of this.