@SJM welcome, it’s a club no-one wants to join. I am sorry.
I was 16 when I was diagnosed, a mature head which makes my experience different that your daughters. I did it all on my own from day 1, it was a shock for my mum and she helped with appointments and emotional support etc but she knows very little about diabetes. She might have felt upset about it as you are now but it didn’t actually impact her life that much and if it did only at the start.
But I have grown up with it and had it more than half of my life now, so I can help with some of what she will face as she grows up.
Don’t panic, you can do this and so can she. Kids are resilient.
Ask questions and do your research from reliable sources, you found the forum which is great. Diabetes UK have loads of support and do JDRF (Breakthrough T1D). Lean on your hospital team.
What I can say is that diabetes won’t stop your daughter living a great life, anything she wants to do she still can. It just takes planning that’s all.
There’s professionals in all sorts of fields now, international sports stars, NASA engineers, singers, models, all emergency services, pilots etc.
We travel the world, look after others, do amazing things.
And we are living longer with less complications, and the treatments are better too which means the day to day and general health is better.
Take care. Try not to beat yourself up about it, nobody’s fault and it’s not using your energy in the best way.