Well, clearly I spoke a bit too soon, or perhaps just underestimated the recuperative powers of The Rat. The little critter is still hanging in there.
Actually, she's shown significant improvements since she first fell ill. The head tilt is gone, manual dexterity is pretty much back to normal. Her balance is still a bit off, but I've put the ramp to the upper platforms back in her cage, seeing as she was climbing up there anyway. Now we just get periodic thumps from her falling off said platforms. Her vision seems the only thing not recovering. I've got to be careful giving her peanuts, as she tends to drop them and then seems to be eyeing my finger. I guess, if your vision sucks, it looks like a peanut.