Looking at the HbA1c levels and their changes I would have said your wife has been Type 2 since at least 2015 , probably before that.
An HbA1c higher than 48 mmol/mol would normally be used to diagnose Type 2. The pancreatic conditions earlier in life may be a contributing factor although the high insulin levels in Jan 2018 (assuming it was a fasting insulin test) shows that insulin is being produced so that kind of discounts Type 1 unless she is having an extremely long and benign honeymoon period.
I've never had any experience of a c-peptitde test so no idea what those levels mean although I'm sure there will be someone along who has..
Bringing HbA1c down by diet alone is usually a sign of Type 2 being controllable and so far as I am aware Type 1 and 3c would not react in this way without meds.
Feel free to shoot me down Im just a fairly well read Type 2 (maybe ex Type 2).