mystery illness!

Question
Hi, I have 7 girls in a very large cage and they all seem very happy and energetic. Thursday I went to feed them and they were all climbing on the sides, excited to see me, except for one girl, Una (born sept 2007) was just lying in the bed. I took her out to look at her and her eyes were very dull and she wasn't moving her nosie to sniff things. Her usually healthy body felt bony. I KNOW that the day before she had been fine, because I always check each and every rat. I put her down on the floor and she was trying to walk but it seemed very difficult for her to use her back legs. I put some food in front of her and she started eating like crazy, but lying down. I rushed her to the vet (which is a 24 hour vet with a huge staff and 3 exotic specialists). They immediately got her onto baytril, tribrissen and fluids. The next day they added metacam and a little cortisone. No one has any idea what is wrong with her, and she has been almost exactly the same since I brought her in thursday night and everyone is stumped. She is still eating, but not seeming to get any worse or better, just hanging out in the corner and looking icky. One vet said she looks like how  you feel when you get the flu. None of my other girls are showing any symptoms at all. I feed them the Suebee's diet and fresh fruits and vegetables and occasionally some whole grain bread. I actually thought she was going to die the day I brought her in, because she was so weak and listeless, and it's so incredibly difficult to know how sick my baby is and not be able to do anything...every time my phone rings I almost have a panic attack because I'm so sure it's going to be the vet with bad news. I call twice a day to check on her, and last night they said she was the same, just resting, but still eating, that she had eaten a few times that day. When I called this morning, the vet said that over night she actually seemed like she was getting better, getting up and around a little bit, and when he came in the early morning he said she looked much better, but soon after she went back to the depressed listeless state. I did get her to the vet the same day that she showed symptoms (which I know in ratties is sometimes too late) but she's still hanging on and I'm just becoming increasingly nervous. Have you ever heard of a very sudden onset of a disease like this? The vet did notice that she doesn't actually seem to be getting "worse" (I don't know how she could get too much worse than she was when I brought her in) but that she is just staying pretty much the same. Any ideas? recommendations? All 3 exotic vets have been trying to figure out how to help and they can't.

Answer
How are things?  I am so sorry this got lost in the email.
Acute illness like this is often a nasty infection, from strep pneumonia that could be subclinical which is why you may not hear lung sounds etc....and also meningitis can act like this as well. Acute onset that can wax and wane.  I would suggest blood work right away. Is she still at the vet clinic now??

If she has not improved, I suggest going full throttle using amakacin and gentocin while the blood work is being processed.
She can also be sedated and be given IV which will get meds into her very fast and since she is at an exotic hospital they will have a tiny gauge needle for this type of procedure no problem.  Fluids can be given this way rather than subcutaneous since a direct line is better than under the skin waiting to be absorbed.  
If you dont mind me asking, what city and state are you in?  I am amazed that they have an ER clinic with three exotic specialists at one facility where the are only 130 of these vets nation wide.  I think California has the most board certified exotic Vets out of any other state, of course, and I believe Texas is a close second.