This statement is at the top of the Dosing Methods Sticky Note:
The dosing methods were developed long before pet meters became a thing.
The goal with SLGS is to keep nadirs between 90 and 149, and the highest numbers, which is often the preshot, at or below 300. She was at that with 0.25 units before you increased. The reason her numbers had started to go higher on 0.25 units previously is that the depot of the 0.5 unit dose you had been giving previously was wearing off. It was not due to the meters. Typically the human meters read lower than pet meters, especially in higher numbers.