She ignores me, then talks to me?

Hmm sounds to me like she's either A) Not that interested in you but when she's bored and has no one else she comes to you. B) She likes you but is playing games with you like to keep you interested and on your toes kinda, I think it's really dumb but I've had friends who did that to their crush. C) It's something completely else...

I can't know for sure what's going on in her head here's just a few things that first came to my mind. Good luck!

Well, that's just rude of her :[ I would give her a taste of her own medicine and tell her you're busy and can't be bothered with her when she comes around.