It’s good you are seeing the vet. Infections can crop up when you stop antibiotics if not all bacteria have been eliminated. That can happen in a closed wound because the bacteria gets in when the wound is open and then they linger, “waiting” for the opportunity to start festering. 9 days or 10 days wont make a significant difference though. As for antibiotic resistance, there is actually no conclusive evidence supporting the claim that stopping a course of antibiotic sooner will increase the risk of antibiotic resistance. All use of antibiotics increases the risk of antibiotic resistance, which doesn’t mean you should not use antibiotics when they are warranted, in your case they absolutely are warranted.
As for physical activity, I agree with the vet. The internal wounds need two wwwks to heal after a normal spay, and Luna’s spay was complicated. The better safe than sorry-principle applies here too in ?