One thing at a time. After you get the curve, we may have a better idea of which way the dose should go. And it's your kitty and you hold the needle. You do what you are comfortable with. We can always start out with a small reduction down or a small step up.
As far as the vet, I think I would figure that he will have a dose while she is being boarded. Then you will bring her home, test and decide on a home dose. They will most likely be different.