Is she a b**tch or is there some other explanation?

ok well some girls can actually be totally oblivious to when people are saying hi to them. so dont take it personal. you never know if she also might be nervous to talk to you, she may secretly have a thing and she is too scared to talk to you. or maybe she just doesn't like you for some reason and she doesnt want to talk to you. try and say hi again, you never know what will happen.