Any thoughts on what may be going on would be greatly appreciated.
I think you need to take the dose up. This isn't getting her into good numbers. I would go up to 4.5, the standard increase with TR, I know you were trying the fattening doses after she dropped into the 30's back in july 2020 and that seemed to work for a while, but it looks to me that is not being effective now and may be a bit to cautious of an approach.
Taking her up too cautiously by fattening dose may be contributing to glucose toxicity, because she spends more time out of the healthy range and there are occasions where you may have waited a bit to long to take the dose up, I get there may have been reasons for that, I'm not critisising it's just an observation from the ss, which may be contributing to her numbers being a bit off.
She's a long term diabetic, so you may need to follow TR a little more closely to get her regulated. Reassess that dose every 6 cycles, if nadirs don't fall into the normal range, take her up 0.25u. I would recommend you post on the forum here regularly to get some dosing help from the experienced members. She's not making it easy for you, so it might help you to have some other eyes on her numbers and help with talking through dosing. You can revisit the fattening and skinny doses if you find it becomes necessary at some point in the future.
Just a heads up if she get's to 5u you would be looking at 0.5 dose changes, think of it as a percentage increase. 0.25u increase when a cat is at 1u is a 25%, 10% when they are at 2.5 increase in dose 0.25 u when a cat is on 5u is only a 5% increase in dose. Hence we move to 0.5u increases to kittys on doses over 5.
The reason I am mentioning it now is that this also applies to fattening a dose, the percentage increase in dose, fattening a 1u dose is much larger, and may be seen to have a greater effect than when you fatten a dose like 4u, the effect will be negligible at best. I hope that makes sense.
She seems normal other than what we believe to be her feline hyperesthesia acting up more
Is there something that might be stressing her more recently?
Appy and activity ok? Are all the 5 p's in place
pooping
playing
preening (not too much in her case)
peeing
purring
Aside from the dosing I would immediately think of having her teeth looked at (if you haven't had that done recently), teeth problems can certainly cause their numbers go up, and often it's difficult to assess.
(She had an extraction in october, so you wouldn't think it was her teeth.... but just wondering if vet thought that some of her other teeth might need attention at a later date)