Aloha from Hawaii,
We will be going to DL in November and we are celebrating my 13yr old daughters B-Day, I am planning on having a few presents wrapped with a note from Mickey wishing her a happy birthday ready when she wakes up the morning of her birthday and since we are staying at the DL hotel I was going to check and see if we can get a call from Mickey wishing her a happy birthday, maybe you can have some presents ready with a note from her favorite character on a homemade letter head with some type of Disney theme, then if you or your husband can make a fake voice maybe one of you can call the hotel room in the morning and wish her a quick happy birthday before she realizes its you. I know my daughter will know that I planned all that because shes much older but I have been taking my kids to Dl for years now and we can't get enough of Disney magic.
Maybe you can also get a birthday hat at the Mad Hatters, thats if you will be going to the park before her actual B-Day and a nice little sweet treat like a cupcake or cake. I hope all goes well, good luck.
Aloha Zena