I don't really know the whole story here as I must have missed your earlier post, but from what you are saying this girl does have some problems and maybe does really have a horrible life, and being like this to you makes her feel better, a type of bullying really isn't it? is there anyway you could turn this around and actually be-friend her, i remember when i was around your age, many moons ago, when i started high school my girlfriend and I had these two girls who were a year younger than us, who just did not like the way we had looked at them or something stupid like that, whenever we saw each other we would glare and whisper and say things, we did it to because they did it to us, but you know in the end we became friends, not great friends, but ended up smiling at one another.

If that is not even an option just keep up with the ignoring and see if she gives up , when she does not get the attention she is seeking from you, she probably will just do that give up, here's hoping and good luck.