sick female rat,

Question
Our class rat was perfectly healthy on Friday and when I returned on Monday(12-22), she was obviously not feeling well.  She was listless,slow to eat and she seemed unstable at times.  She is drinking and eating, yet she doesn't seem as enthusiastic about eating.  She  tends to doze off frequently.  She felt cold when we first picked her up on Monday. She appears to be thinner than normal.  I do not see any discharge from her nose or eyes and she seems to be breathing without difficulty. We also have another female rat in the cage with her that seems healthy.  She is a class pet and very much loved.  Please give me any advice you can.  She is approximately 10 to 12 months old.  Thank You!

Answer
She should see a vet. Rats can have acute infection that can bring them downhill real fast and before you know it, your rat has full blown pneumonia or something that is acute with rats.
 
Do you have an exotic Vet?        
I dont mean a general vet that sees rats but instead, a certified exotic vet . Let me know where your located and I will be happy to give you some names of good vets. She should see one right away.
I would offer her baby food, letting her lick from your fingers if needed,and  if she isnt drinking she can get liquids from the baby food. She probably has a secondary infection and needs a vet and since rats decline fast, I would not wait long to see if she is going to work this out on her own. Rarely  does that occur, as nice as that would be, its just not really common for rats to get over things on their own.