Happy Birthday to your daughter!
If she likes princesses, then I would suggest breakfast at Norway’s Akershus Royal Banquet Hall or
Cinderella's Royal Table. If Mary Poppins is a favorite for her, I would suggest 1900 Park Fare at the Grand Floridian.
Perhaps you could spend the morning in Fantasyland, visit Ariel's Grotto and then have a late breakfast at Cinderella's. Dining with Cinderella in the castle requires reservations which are sometimes difficult to obtain. Call 407-WDW-DINE (407-939-3463) to secure your Advanced Dining Reservation.
You can order a cake to enjoy at any restaurant by calling the Cake Hotline (yes there is such at thing at the Happiest Place on Earth) at 407-827-2253. Remember to give 48 hours advance notice.
Stop in at Guest Services in City Hall at the Magic Kingdom and ask for a birthday button. Tell your hostess and server that your daughter is celebrating her birthday.
Don't forget to tell the Princesses that your Princess is having a birthday. They are sure to wish her a happy day!