Very cool! Are you doing anything special for her birthday? We ordered a cake but I'm not sure what else we could do. We did note when booking our cruise that it was her birthday. My DD doesn't know about the trip yet. We plan to surprise her the morning of the 10th!
As soon as we get on board, we are going to guest services to get her "it's my birthday" button. We are going to bring some of her smaller gifts to open on her actually birthday, and I'm sure she will have a bigger than normal on board spending account with mommy & daddy

! We didn't order a special cake because she really only likes frosting off cupcakes or ice cream, so I thought I would talk to our server the first night about a special ice cream birthday cake!
I made some special birthday magnets for our cabin door & went with the minnie birthday hat for the port hole this year. I called to see if we could bring balloons, but we can't. So I think maybe some bubbles for her to play with on our balcony or out on deck.
We are also partcipating in the FE gift exchange, so that we be very exciting for her to gifts from others too.
They typically have the princess gathering the first at sea day (which is her bday) so that will be a special birthday treat too. Also, when we pick up the b-day button we are going to get tickets to Tea with Alice.
At WDW we booked the Hollywood Studios breakfast @ Hollywood & Vine. The Disney Jr show has recently added her 2 favorites -Sofia the First & Doc McStuffins.
So it is just a week long birthday for her this year

!
That is so cool surprising her, I couldn't keep anything this big for that long

! I think they do something special in the kid's club too, like cake & sing on their birthday but I'm not sure...and I can't bank on DD spending time there until she checks it out and decides it is something she wants to do - i think she will want to, but you just never know. Last year it took until the 5th night of a 5 night cruise to give Minnie & Mickey high 5's!