Ex text me today after a year. What could she be thinking?

Me and my ex gf (ex best friend) split up january 2012 and around november the same year we had a nasty argument and she told me not to speak to her again. She hasnt contacted me since and I havnt contacted her, she didn't even say or wish me a happy birthday last year. Saying this I was a little surprised when she sent me a message yesterday saying happy birthday completely out of the blue. Im prob reading too much into this and have no intention of getting back with her or anything but does it sound like she misses me or is she just being polite? No smart comments please.