Why is my teacher mean to me? :/?

I had a teacher at school that used to pick her favorites and was mean to a selected few I was one she was mean to I did not rise to it but made a note of everything she did then took it to my principle everything changed after that as many other people had complained about her, don't rise to it and get yourself in to trouble just keep a note of everything she does so when the time comes to take it further you know exactly what to say.