I really want to hope the 375 was a bad reading, but it's entirely possible that's what it is. I don't know that there is anything to make sense of - she's just decided she needs more insulin again, so doing the quick 0.1u increases is a good way to go. Now as for why she needs the increases again: the three most likely scenarios are pancreatitis, a dental issue, or a squirrel. Do you ever notice her losing her appetite and acting a little off? In cats with severe pancreatitis, they'll completely stop eating and get into serious trouble, but it's also possible to have a milder version that is harder to detect, but you can see it in the up and down dosing needs. There's really not much to be done for it if that were the case, but thought I'd toss it out there as a possibility.
Dental issues can cause a rise in numbers too, so if a vet hasn't given a good careful look at her teeth recently, you might have them do so at the next visit, or do so yourself and see if you notice anything that looks irritated. Most of a cat's tooth problems are under the gum and need an x-ray, but there will usually be some sort of gum redness/irritation that hints at it.
And the third most likely scenario is what Rachel calls, "Look! A Squirrel!" syndrome. Meaning it's just one of those things, and while it of course has some physiological cause, we probably won't know what it is, and won't be able to do anything about it anyway. It could be stress, arthritis, dehydration, bad sleep, an upset stomach...a zillion different things. Or it can just be that the diabetes is progressing.
Also keep in mind that not that long ago she was at 2u and still wasn't actually regulated. She had some good cycles and some bad cycles, but 2u was a pretty normal range for her just a couple of weeks ago. It could be she's just heading back into that range again.
So all that to say: it could be anything, and for now you just have to treat the numbers and keep an eye on her (as you always do!). If some other symptom pops up you can pursue it, but otherwise just keep doing what you're doing, and raise the dose until she gives you a reason to slow down or reduce again.