GIRLS PLZ HELP!!!!! why didnt she even say hi to me?

im not trying to sound rude or anything but the very last thing you put explains her whole behavior, shes a 15 year old immature freshman i am a senior in high school i was a freshman once and i have watched the freshman come into high school my sophomore, junior, and senior year and 95% of them act like that. either she thinks shes being cute and that you will keep chasing her or shes just slutty or flirtatious and doesn't really care to have a serious relationship or a relationship at all.