Good to know on the schedule and that you do have a couple days you can get more data. It may be hard, but if there is anyway to change the schedule so you can get a +2 before leaving for work, instead of +1.5, it would be a more useful data point. Ditto for the PM test. If you see a drop to +2, it can tell you to leave a bit higher carb food out for her to graze on. Making sure she has food out at her lowest points in the cycle will be what keeps her safe while you are gone. Some people get autofeeders and have them open a bit before the nadir or low points in the cycle to make sure there is fresh food around then.
Sounds like your vet isn't going to be too involved in dosing. We do have a couple dosing methods we have here that can help you decide (initially with our help), how to change her dose. A cat's insulin needs can change a LOT in two months, a curve once a week is much better.
The depot takes 5-7 days to build when you start giving insulin. When you do increases, it is more like 3-5 days. When you lower the dose, the larger depot doesn't go away right away, it can take 4-6 cycles (2/3 days) to stop influencing the cycles.
She should not steadily be in the high 200's. It depends on what your goals are for her, but you'd definitely like to see her spending more time in lower numbers. Our Start Low Go Slow dosing method says that ideal is when their lowest points during the cycles is in the 90-149 range. Below 90 you reduce the dose, which is why I suggested a dose reduction with that 73. A full one unit reduction may have been too much of a reduction. Normally we reduce by 0.25 units at a time. Yes, we eyeball that with the 1/2 unit markings on the syringe.