@lcsj Thank goodness! Ok, this is a really big diagnosis, but you will learn all about it. Unfortunately, you and your DD are in it for the long haul so you will take your time and gain experience. It might help to write a list of questions for the diabetes nurse tomorrow.
They may have explained to you that your DD is not producing sufficient levels of insulin now, so she will have to inject insulin instead. Things like food (mainly carbohydrates - starches and sugars), stress and growth raise blood glucose levels, so they need insulin to bring them down. You should be taught how to help her manage mealtimes, exercise and sickness which are some big things which affect her levels. The DSN should be talking to you regularly as her doses will need a lot of adjusting in the beginning. She will also need a plan for going back to school. You and your DD should be offered psychological support, but sadly not all hospitals offer this.
There are a few facebook groups that you might find it useful to join as you will get a lot of support - Parents of Children with Type One Diabetes is one, UK CWD is another. You might want to ask your nurse about any support groups in your area, but again, this can be patchy.
It's going to be OK, but it is a period of adjustment and you should allow yourself to grieve when you are not with your DD.