Sounds like a plan. If it helps to reassure you, you’re not going to hurt your cat with a few days worth of pepcid, I promise. It may help or it may not, but it’s not going to cause any harm. And no vet is going to be upset that you gave it either, probably not under any circumstances but especially not in this case. Her bloodwork is fine, she’s showing signs of nausea, and it’s an OTC drug with cat doses readily available online. It’s a sensible thing to try, though you can always wait to talk to the vet first if it will make you feel better. Good luck!