They may eat an enormous breakfast and snack, then very little the rest of the day. They may eat only one or two food items at a meal. Children are erratic eaters because they are very sensitive to their hunger and appetite. They will even stop in the middle of a bowl of ice cream if they get full. Children know how much they need to eat.
Every child grows differently and every child needs a different amount of food.
Some days children are hungry and some days they aren't. Some days they are active and some days they aren't. You have to trust that they know how much they need to eat. You can tell that your child knows how much to eat by the way she grows. If your child's growth shows a consistent pattern and you are offering her a variety of nutritious food in a friendly fashion, she is doing fine.