What does it mean when a girl talks about her celebrity crushes around you but doesn't pay you any mind?

It means she's self-absorbed in her little fantasy world and probably isn't ready to have any kind of mature relationship with a person who's available and right in front of her. :)

Does she talk TO you about it? Or does she just talk in your presence in other social situations? The former might suggest that she has some interest in you personally, and can't figure out a way to have a conversation with you.