I surprised my daughter for her 6th birthday by flying her down for a "girls weekend" 3 years ago. Thanks to the people on the DIS, I got lots of great ideas. 1. Make sure it's on all your reservations that it is her birthday.
2. Ask for a character wake-up call.
3. Make sure she has the button! One CM noticed it, mentioned to my daughter that Goofy had been waiting for her, he picked up a phone, and Goofy was on the other end singing Happy Birthday. It was great!
4. Eat at 1900 Park Fare in the GF. I had pre-ordered a birthday cake with a white chocolate Cinderella's Castle on the top. The best part was that Prince Charming delivered it to her while singing Happy Birthday! Needless to say, my daughter was stunned! (Not to mention the cake was fantastic!)
Anyway, we are now headed back for DS's 6th birthday followed 4 days later by DD's 9th birthday. I'm trying to think of special things for DS since DD had such a special time on her 6th.
I hope my suggestions are helpful, Disney really knows how to make birthdays special. Oh, another thing.......I had read prior to DD's last birthday trip not to expect anything special for her birthday, that it all depended on the CM's. Good advice, that way you won't be disappointed, however, my DD was made to feel like a princess for our entire 3 days and she still talks about that trip 3 years later! It was worth every dime!