Baby mouse exposed to sickness

Question
Greetings, I have a little bit of background to tell you before I can ask my question.
   About three weeks ago I became a mouse mother to a 5-6 day old infant mouse. Many late night feedings and stressful days later and I had a beautiful mouse beginning her weaning journey. I thought now would be the best time to get her a friend (of an equivalent age) so that by the time quarantine on the new mouse was over my little baby would be bigger and eating on her own.
I went back to the same pet store and got another mouse. The pet store was/is not that great, strong odor of pee that makes you dizzy after five minutes, does with back to back litters, etc. I picked one who seemed healthy and brought her home. Within an hour of her being home I noticed a constant clicking noise; Scheduled an appointment for the vets next day and was honestly quite hopeful because she was active and eating. She stopped eating and drinking soon there after. Vet prescribed Sulkaprim which I could find no information on the internet about and was guessing that it could be either myco-something or Sendai virus. In any case, I stupidly housed the two mice not together but sharing the same air space (two ten gallon tanks next to each other). Sadly, the new mouse didn't respond to the antibiotics, got bouts of diarrhea while still refusing any water or food and died. :(
     HERE IS MY QUESTION! (thank you for your patience) My hand raised mouse is showing no symptoms of the same illness, she's active, eating and interacting with me as per usual. She was most likely exposed to whatever caused the death of the second mouse since they were living in the same environment at the pet store and then re-exposed to the illness when I brought home the second mouse. She is my first mouse ever so I have no baseline for "normal". She does make a clicking noise intermittently but nothing like the constant chatter that the second mouse emitted. Is this okay or should I seek medical attention for her? How long before she would start showing signs of illness do you think? They were next to one another for about four days. I know I need to act fast, especially when they are so small. I can't believe how rapidly the second mouse went downhill. I don't think I could stand to lose another. Thank you for any input you might have.
-One very worried mouse mother.

Answer
Dear Heidi,

Myco is the best case scenario because every mouse has it anyway-- which doesn't make it less deadly but at least it is easily curable if you get the mouse on antibiotics in time.

Sendai is the worst case scenario for all the mice in your town, because it spreads like wildfire and can kill entire mischiefs and colonies of mice. You need to know if it is sendai because the pet store needs to know- only a very, very unscrupulous pet store or breeder would let an animal go with sendai. Still, in an individual case, some animals can survive after a course of antibiotics.

Yes, bring her to the vet *right away.* You need a vet trained in 'pocket pets' or 'exotics.'  I don't know anything about sulfaprim, except that it is not a common drug, which is why i wonder if you have a good exotics vet.

If you need to find a vet, try here:

http://www.aemv.org/vetlist.cfm

If you are on Facebook and join my group Rats and Mice are Awesome:

https://www.facebook.com/groups/RatsandMiceareAwesome/

We can find out for you what sulfaprim is for :)  and you will have an even quicker way to get an answer next time. :)

Best of luck to the little girl. Chances are the vet can put her on an antibiotic and she will be fine. But with such a little treasure you want to act fast.

Squeaks,

Natasha