I would hold off on the gravy unless you see a number in the 50 range. That is considered the "low end" of normal. Great that you are prepared though! I would wait until +6 to test, but sooner if she starts acting weird, like howling or drunk looking. I think she'll be fine though, but I am online so just holler! The first defense is just to give a spoonful of low carb, test in 15 minutes, then break out the gravy if the number is lower. But only a spoonful at a time. If hypos last a while (which doesn't happen all too often with PZI/Prozinc, keeping them somewhat hungry is helpful, in case you have to continue to feed. That seems to happen more with lantus from the "hypos" I've watched as they happen. Lisa (and Cassie) had one that lasted a few hours the other night, but that was the first time I've watched a PZI kitty take more than an hour before they started climbing.
Carl