Firstly, may I say how sorry I am that you are having to deal with diabetes in such a young child. It would be so much easier if she were just a few years older. Having said that, you do have an opportunity to influence her diet choices so she never gets addicted to sugar.
100g strawberries has 8g of carb, so actually it isn't a bad choice....
15g is actually a reasonable amount of carb for a snack, as long as it isn't biscuits or sweets.
Can I ask, do you have other children? It's going to be a lot easier to make healthier choices for her if the whole family is doing it....