You could also order her a specialty dessert. There is a chocolate slipper dessert that is available at both Cinderella's Royal Table and the Grand Floridian. It's a chocolate shoe with several swirls of whipped cream, raspberries and coulis to garnish. I think you have the option of either white chocolate or milk chocolate and the dessert is only about $12, as opposed to the pricier costs of cakes.
And, now "Something Grey" (the dessert Lumiere sings about in the famous song) is available on the Be Our Guest menu--so you could order her this chocolate mousse speciality dessert, which I think goes for about $5?
And, if you have any character dining reservations, be sure to tell them about your daughter's birthday and the characters will supply her with an autographed birthday card. Just another little bit of pixie dust for her special day.
Also--go to Guest Services and get her a complimentary "It's My Birthday" button. I'm sure you've already heard of this--but what a nice way to celebrate. Everyone will wish her a happy birthday and treat her extra special!