I was diagnosed with Type 1 at the age of 13 and am now 68. I had two children, and now have two granddaughters, none of whom has got diabetes so far.
Treatment and testing is SO much better nowadays, although injected or pumped insulin is still essential for Type 1.
Currently they are working on a closed loop pump, which tests your blood sugar and automatically doses with insulin, so the days of having to decide on how much insulin to take when will be gone. Basically it will do what the destroyed pancreas cells used to do, so life will be as close to normal as possible. It will be a complete game changer!
www.diabetes.org.uk/about_us/news/new-findings-nhs-hybrid-closed-loop-pilot-dukpc-research-highlights
I currently use the Libre 2 which I get on prescription. It has made a huge difference to me, as it has alarms available for too high or too low blood glucose, which will be so helpful to your granddaughter and her parents, especially at night and at school.
www.freestyle.abbott/uk-en/products/freestyle-libre-2.html
I have never used a pump, preferring to inject myself, but diabetics I know are very happy with theirs.
There is obviously no good time to be diagnosed with diabetes, but the treatment and monitoring are SO much easier now; I feel sorry for the 13 year old me and my mum having to navigate it with no means of testing accurately!
She truly can live a very normal life, and I wish you all the very best!