I have a T1 daughter that just turned 6 - we've been dealing with diabetes since she was 2. It is so, so overwhelming in the beginning. I promise you that it does get easier. I second the recommendation for "Think Like a Pancreas" - excellent resource for living with diabetes.
Illness is so incredibly different in a diabetic child. We're several years in and I still get a little panicky when she has so much as a sniffle. We've had some really rough patches and she's been through a multitude of random illnesses. I've learned that as long as she isn't vomiting and there are no ketones, we're good. In fact, we can now tell when she is getting sick because we see a sustained and consistent drop and spike of a day each for the 2 days preceding the symptoms. Convenient as all get-out, which is why I took my asymptomatic daughter to the doctor today...and he found the raging case of strep throat that has her tonsils coated and *this* close to touching.
As to the vax decision...I don't believe that there is one answer for everyone. We think about it every year and have decided to handle it year-to-year. One year, we opted for a flu vaccine. She'd been through a really rough 2 months at the start of flu season and everything she had led to the hospital and to many, many scary days and nights for all of us. Fearing that the worse was yet to come, we took her in for the shot (well, shots...it's 2 the first year). Never regretted it. That was when she was 4. Every other year (2, 3, 5, 6) we have passed on the vax. This year we are passing on the flu shot and the h1n1 version. We homeschool, the kids are out of daycare and DH and I are not employed in fields with higher than normal levels of exposure. If any of that were different, we might have decided differently.
What does her ped endo say? Ours asked if she had it and we said that she hadn't and that was it, so I asked. They were completely indifferent and never gave me a word of warning or any recommendation to change our minds. Had they been concerned, it would have given me reason to rethink it as I value their opinions based on their experiences.
If you haven't posted this on the SN boards, you might want to try the question there as having special needs can change your outlook on a lot of things. The diabetes is the issue, not the vax, in my opinion, and you might get more insight over there. I happened to see this in new posts but a lot of people may not