What does she like to eat?
It doesn't have to be a traditional breakfast such as cereal or toast, how about a sandwich? Low sugar yogurt, beans on toast,
A good cereal for me is the mini shredded wheat.
As above, carb count is important, one serving of shredded wheat is about 40g carbs, but the box has those details on.
get a good set of digital scales to weigh everything until you get an idea of how much a "portion" represents