I guess your family is already following whatever advice the hospital diabetes nurses gave you.
What age is your daughter? If she is a baby or a toddler, the advice from the diabetes team used to be to watch how much of her food she has eaten, and then inject insulin immediately after the food. However, it is important that you learn carbohydrate counting.
If she is older, then she will do carbohydrate counting for her portion of food and inject prior to the meal.