"Just a cold" is highly unlikely, hun.
As a defense mechanism (to keep quiet and not look like "the weak one" of the pack), mice will hide their symptoms until they no longer can. If Sterling sounds/looks sick, she's been sick for a while. My rule of thumb is that anytime I have an inkling that something is wrong with a mouse, 99% of the time I'm right, and I end up feeling very grateful that I visited a vet over something that other people had tried to convince me was "nothing", "no big deal". People who say things like that don't know anything about mice. You are right, Sterling needs to see a vet AS SOON as you get back. Set up an appointment while you are away, just to be sure they have space to assist you.
Also if you did not quarantine Sterling, her cagemates are already sick too. But bring Sterling only to the vet, so you will only have to pay for one mouse to be seen; let the doctor know you have other mice and they should give you enough medicine for the others. Don't pay for cultures either unless you feel there are bigger problems going on, cultures tack on hundreds to the bill.
DO NOT ACCEPT T.M.S as a treatment. T.M.S. is also an anti-biotic, but it is dangerous. My favorite little girl had an allergic/anaphylactic reaction to it and she died a slow, horrible death. Ask specifically for Baytril if it ends up being some sort of URI.
I'm guessing it will cost around $60 this route. But I think it's worth it, especially for so beautiful a girl as Sterling. I'm assuming you breed or have had mice as pets for a while now; I'm sure you realize that mice make the best pets when they are completely healthy.
Good Luck, give Sterling my love.