Firstly, diagnosis usually works as follows: If you're a child or have acute DKA, then you're T1; else you're T2. So there is plenty of margin for error since we're both starting to see adults with late onset T1 and children with T2.
She said there was no such thing.
She's arguably correct here since the definition for T1 doesn't have an age limit.
I assume the early treatment is the same.
I think that early insulin treatment works better; the alternative would be putting you on more and more ineffective medication and waiting for it to fail before ultimately starting insulin therapy. Initially, it will sorta work - exercise and Metformin increase insulin sensitivity (making the insufficient insulin go further), and other drugs increase insulin secretion. If you do have T1.5, however, more and more of the pancreas will be destroyed and these drugs will stop working.
If nothing else, it will be better psychologically to make sure you have efficient treatment now.
Ask the doc. for some simple tests that will indicate what sort you are. I say indicate because you can be a T1 with T2 a bit as well. Or then you might be T2 with a bit of T1.
I'm not quite sure what you mean by this. For T1/LADA/T1.5, there are primarily two tests: GAD antibodies and C-peptide. T1 is an autoimmune condition, and GAD antibodies are usually but now always present; they are not present in T2 patients. The C-peptide relates to insulin production and you'd expect a low result in T1/T1.5/LADA patients only; T2 patients produce normal amounts of insulin but it doesn't work effectively.
If they come back positive, then you definitely have a T1-spectrum condition.
Testing for insulin resistance directly is possible as well (glucose clamp - simultaneous glucose and insulin IV adjusted to give stable BG and settings are compared to reference values) but this is mostly done for clinical studies.