all of the above happens - giving insulin and testing becomes incredibly easy and doesn't take much time at all. Some cats go off of insulin, some don't. my cat had acromegaly - he never went off of insulin, even after we had it treated with radiation, but he had a great quality of life until the last 3 days. Cats with acromegaly can be difficult to get regulated - the tumor that causes it can pulsate in its hormone output, which means that they go up and they go down - or not. just depends on the cat. He got up to 15.5u of insulin per shot before the radiation.
There are tricks for keeping the cost down - i bought 4 boxes of pens on Craigslist from an adult daughter whose 90 yr old diabetic father had passed away. I listened to the story, i met her, and it all seemed legit and the insulin was fine. You have to be cautious, there, however.
While his blood sugar still had highs, true, he didn't die from diabetes or from acromegaly. We think he had cancer and he was really relatively healthy for a senior cat with a chronic disease until that last week.
As you get closer to the right dose, her symptoms will improve to the point where you may not see anything to say she's diabetic except the syringes on the counter.
After listening to your story and looking at Fay's ss, I don't really think she's overdosed. People will continue to suggest it to you because no one is going to go back and read all the previous posts, but you explained it well and i suspect it's in the ballpark. It's only "quite high" for a regular diabetic cat. For a cat with a high dose condition, it's not high at all. Now, saying that, I have no idea if Fay is a high dose cat or not - I'm just trying to put it in perspective and let you know that there are reasons for some cats needing more insulin than others.
If you want certainty on her dose, you'd drop back to a weight-based amount and hold the dose there for several days to let the counterregulatory hormones clear out. That choice can only be yours, but if you want to do that, we can certainly guide you in it.
There isn't anyone here who doesn't understand your frustration and discouragement Alex. What we can tell you, from this end of the Sugar Dance, is that it does get easier.