Sometimes even in people we have to try to figure out if they're in pain when they can't tell us. There are signs.
I googled around a bit to try to help you figure this out. I think your instincts may be correct about the Tram as long as there isn't anything else going on with Clara in terms of infection (surgical incision, UTI), she's eating, drinking, peeing and pooping normally, and otherwise seems ok.
This, I thought, was a good article for you to read:
https://metro-vet.com/references/post-operative-management-at-home/
The gabapentin needs to be weaned when you do take her off of it. It helps enhance the other pain meds and should make her a little drowsy, if anything.
Here are signs of pain in animals:
a reputable veterinarian would know the specific signs to ask about or look for such as restlessness, heavy panting, shaking, whining or constant meowing, dilated eyes, fast heart rate, salivation, poor appetite, lethargy, limping, hiding, and behavioral changes.
(Took out link as it wouldn't let me post w whole word for Tram, but it's under Tram facts)