She is 6 and a half years old. She takes food six times a day to meet her insulin which is 10 units of Mixtard 10 given once in the morning. Having diabetes does not change that fact that six year olds like to snack.
Children still have relatively small stomachs at that age and are usually quite active.
The combination of these two factors generally leads to youngsters wanting snacks. You don't mention whether or not you are testing blood glucose at home. It's an invaluable tool for gathering helpful information in situations like this. Particularly since your child is receiving only one injection of insulin daily, it is actually helpful to spread her food intake rather evenly through the day. This will help minimize wide swings in the blood glucose caused by a mismatch between insulin and food.