If I remember correctly, you just brought home new rats. Rats, just like people, can get sick if they're stressed, especially when brought to new environments. Whenever I bring home rats, they typically have "new home sneezes" which should clear up pretty quickly. If sneezing goes on longer than about a week or two, I get concerned. If you see prophyrin or puffy fur, then your rat is most definitely sick. Since you're already taking Alley to a vet, talk to this vet about her sneezes, mention the new rats, and how they're doing.
You should also listen to Alley's lungs. We call it "rat phoning" because you quite literally bring the rat up to your ear and listen to their breathing. Depending on your rat (some may not tolerate this), press their side up to your ear. Usually, I try to put my ear right into their little armpit and listen. This is best done when the rat is calm. Pressing their chest right up to your ear, where the sternum is pressed against you, will only let you hear their heart.
If they sound watery, congested, or their breathing just seems off, it's time to be concerned.
Also, occasional is quite vague. Do you mean once a day, once every other day, how often would you say it is? Because rats, like people, sometimes just sneeze because their noses got tickled or their whiskers did. If anything, it never hurts to talk to your vet about it, especially since you're bringing Alley in anyways.