Kristin,
It's difficult to suggest what to do. Not that many people here have any experience with using the Humulin/Novolin N.
First, I'd suggest another test to see what Calley's current BG levels are.
If you are confident that Calley will keep her food down, you might try giving a token dose of 1U insulin. If she were my cat, I'd stay up and monitor her, getting BG tests at +1 and probably +2. More tests may be needed.
You may not be able to stay up with Calley and monitor her. If not, you may want to skip the shot.
The problem is, that not enough food, not enough insulin and an infection which can be hidden, can lead to serious consequences, like DKA. It's a judgment call, and you are the best judge of how she will react.
Since the Humulin/Novolin is so short acting, giving a late shot will not throw off your usual schedule.
So, you need to ask yourself, do you have plenty of test strips, karo syrup or other simple sugar to raise those BG levels if needed, do you have the time to stay up and monitor. Then make your decision.