I'd never heard of that test before.... they may have mentioned it the first time around but once the doc said if she makes it until the morning she has a chance, I sort of blanked out. No idea what triggered the change. She was I ketosis I remember that as they thought at first she would have kidney problems. I actually think it may have been a kidney infection that started this all as she did end up having to get a drain put in and heavy antibiotics after she got out one time.
An HbA1C test is used to diagnose diabetes, to monitor ongoing management and determine suitable medication. I would expect that she would have had that on a regular basis to make sure her medication was keeping her blood glucose at acceptable level. It measures in simple terms the average blood glucose over the previous 3 months and well managed condition the level would be below 48mmol/mol.
This is a different test from the finger prick testing which just show that moment in time and it will go up and down throughout the day and night usually in response to food and exercise but other factors as well. The range for somebody who is well managed would be 4-7 fasting and before meals and no more than 8-8.5 2 hours after meals. As you rightly say many who are Type 2 will manage their condition with diet and a variety of oral medications but for some people those do not work well enough and they may then need insulin either instead of or as well as.
People who are Type 1 will always need insulin but sometimes they may have oral meds as well, it is a very different condition being autoimmune.
Sometimes people are assumed to be Type 2 but are actually misdiagnosed and tests will show they are actually Type 1 which is not just in children or young people but can develop in mature people, I have a friend who was diagnosed as Type 1 at nearly 80 years old after treatment for 2 years as Type 2 did not work.
There are a few other situations when people will become diabetic, damage or removal of their pancreas or steroid induces diabetes and again they will have specific treatment requirements.
You may find a look at the Learning Zone (orange tab at the top) will be helpful.
I also suggest you ring the help line number at the top