I always tested Bob, and right after the test, I would give him his food ("reward for the poke"). As soon as he was done eating (10 minutes, tops), he would get his shot. The shot he never minded. At first, he didn't like tests, but with either a meal or a treat right after the test, he quickly learned that there was a reward for putting up with me. ;-)
Once you test, you know whether or not she's going to need a shot. If you decide that "yes, the number is a shootable number" then feed her, and if it takes a half an hour for her to eat, that's fine. Lots of people actually shoot the insulin while the cat is eating, and the cat doesn't even know or care if they are distracted by eating. I always waited till Bob was done, since he cleaned the bowl so quickly anyway. It is important that you know she's eaten sufficiently, because you want some food on board to make sure the insulin isn't going into a kittie with an empty tummy. That's really important when you are getting a number that is right on the borderline of "do I shoot, or don't I?"
Carl