If your daughter is over 3 but under 10, then she is considered a child for purposes of the dining plan and you are not supposed to use her credits (child) to pay for adult meals. That said, if she is 10 or over and you are paying adult prices for her, then if you want to order 2 meals for 3 people and save a credit to be used later on for another adult meal, that is fine.
The child plan costs $10.99/day and the adult costs $37.99/day. At buffets, you will be charged one credit for each person in the party. Only children under 3 can share at AYCE or family style restaurants.