Advice needed for child with diabetes

Hey everyone, my 5 (4 at the time) year old daughter had a glucose test last year. It was the kind where they pricked her finger. The first prick came out to be a level of 177(extremely high), they gave her a popsicle and a sucker, tested her again and it came out to 55 (too low). They said they would check again within a few months. So last week we had a full panel (non fasting) and her glucose was 137, she only had a few bites of Special K cereal 2 hours before the test. They have to retest her again (fasting) to verify the results.

My question is, how do I explain this to her? How do I explain the sudden diet and lifestyle change? Can she still eat school food or should I pack her lunch? If you have a young child with diabetes, what types of snacks, drinks and food do you give them?

Thank you so much in advance for any advice!