My daughter is a little older at 10 but she was diagnosed in February this year and was back to school after just 2 weeks.
Her DN held a meeting with all the school staff and explained Ellie's diabetes to them. She then held a further meeting with Ellie's teacher and school nurse/first aider where she went into things in greater detail. How to use her equipment, help her with injections, treat a hypo etc. It turned out that there was already a boy younger than Ellie with T1 that was using a pump.
When Ellie first started back at school I was a wreck but I shouldn't of been so worried as everything went quite smoothly. The school nurse kept me informed of how Ellie's first few days were going, more for my reassurance than anything.
It's been a huge weight off my mind knowing that Ellie is safe in school and the staff all know how to help her if need be.
Ellie also carries a note book with her where the school nurse records Ellie's bloods/insulin throughout the day and if she's been feeling unwell etc, I also use it to send info back to school regarding any illness, changes to insulin ratios, what carbs are in her packed lunch etc.
It might be worth a meeting with the school regarding your daughters diabetes before she starts even if it's only for your reassurance.
Hope her first day at school goes well for you both