I should note that during the meet and greet you will only meet 3 princesses (and/or female heroines that are not princesses such as Mulan, Pocahantas and occasionally Minnie Mouse dressed as a princess). You have no idea who will be doing the meet and greet when your turn comes. They rotate out randomly and you cannot wait to the side until a certain one comes in.
So, if your child has her heart set on seeing a certain princess, please be aware that the PFF is not a guaranteed way to meet that princess. You may even find that the one your child wants to meet rotates out right before your child's turn comes.