I think you can receive a birthday sticker from Guest Services.
A friend of mine has had an annual pass for a good 12 (I think) years and on his birthday, he was told to go to Guest Services when he got to the park. He was offered either a free dessert, free express (some onesies, but with 2 or 3 barcodes on each for how ever many he had in his party), and something else that I can't remember. So I guess if you have an annual pass for awhile, you get different benefits.
You could always buy her a birthday hat.

They're pretty cool!