It might help to know how insulin works in a non-diabetic.
Normally the pancreas just chugs along putting out a little insulin, roughly constant, to keep the body happy. The constant (low-level) amount is about, say, 25-30% of total pancreas capacity.
When food comes in, the pancreas swings into action, cranking out 50% or up to 100% of capacity, to keep blood sugar down and send the excess sugar into the cells, where it's either used or turned into fat for later.
Within an hour or two, blood sugar is back to normal, and the pancreas goes back to its normal (basal) production level.
It seems a diabetic cat is first able to go off the juice when their pancreas is healed to the point of producing maybe 40-50% capacity. This can not only produce a basal insulin level, but can handle some food spikes.
But the speed of bringing those spikes down will be reduced! Without 100% insulin production available, the blood sugar will remain high for longer than in a healthy cat. When that sugar is 'high enough', its concentration in the blood physically burns the beta cells and damages them, reducing their capacity a bit, and slowing or reversing healing. If that happens, her numbers will rise further and she's likely to lose her remission.
Bottom line: Her numbers are creeping up slowly because her pancreas is still a bit on the low-production side. If you can keep her numbers from getting into the 'burn' range for a few more weeks, the pancreas will keep healing and she'll be able to take it on her own. For now, you're the training wheels.
At some point those numbers may (or may not) get high enough for a smidge of insulin to help. I don't know (and I don't think anyone knows) what the threshold is before I'd help out, or how much insulin I'd give to make up the shortfall. But there's a right number for both of those, for Chloe.
A radical suggestion that might be a bit much, and is not medically 'necessary':
For any creature, there's a safe amount of insulin you can give, because it's just too small to matter. When you're around to test, try some tiny experiments with micro-doses and a glucometer, trying to find a dose that lowers her blood sugar by just 20-30 points at whatever ProZinc's peak time is in Chloe... (Start with the zero line on the syringe and work up to 0.1, 0.2, etc)
Once you have a good idea of that dose, you can give it when she runs over 110...