You're casual friends, which is what I'm saying. How many people wished you a happy birthday that you don't even talk to anymore? Probably a lot, it means hardly anything.
Look, this is your ego talking. It's trying to convince you that she had a sudden moment of clarity and suddenly realized, "omg I was wrong to push cityboy away, I actually AM attracted to him!!" But that's not how girls work.
She's not on the Cosmopolitan forums starting threads on "How do I get him back?" and all her girlfriends tell her to write Happy Birthday on your Facebook.
In reality, she's probably wondering why you haven't reached out to her yet, because she figured you'd be on her doorstep with a dozen roses already. Don't do anything. If she initiates any contact over the phone, immediately tell her to come over, and if she declines, go back to ignoring her.