Why is she acting this way?

Ok so this girl asked me to a dance where girls ask guys and i said yes... a few months before, we went to homecoming together and have hung out every weekend, and talked on the phone almost every night and flirted. since i said yes to going with her, she has been actin weird at school. the other day we were sitting in cl and she was talking to one of my friends and i was sittin right there and she would only say a few things to me and would not look at me much...she is fine around other people but not me anymore... outside of school she usually acts normal when its just us hangin out too, every day after school she hugs me and says "call me later" cause she always wants to talk. why then is she ignoring me during school when other people are around?