Her favorite princess Aurora. One of Ellery's questions to Aurora was, "How do you get the sweaters on the owls?!"
Cinderella. Ellery was a little distracted because they were announcing another princess entering the room. Ellery also told Cinderella that she is not her favorite princess.
Oh, and I have to mention that Lulu got teary-eyed when they began announcing the princesses and queuing the music! The magic of Disney!