What does it mean when a girl ignores, or looks at you and won't say hi?

I've known this girl for a while, I hardly see her now a days, but before she would either ignore me or sometimes say hi, and always ask about my girlfriend. But then when I would try to talk to her she wouldn't say much. It was like she had to initiate the conversation first if she was going to talk to me. Now, if we see each other we will just lock eyes and not say anything. I can't read this girl what so ever.