Smokey just added the felinecrf website which is excellent.
I am afraid Fern's fur already looks ruffled in a way that points to kidneys.
If the sub-q fluids don't work she may need IV for a night or so. I hope very much she overcomes this crisis.
Of course eating is very important for kidney kitties. In Filou's bad times I always had success with egg yolk which was more than one time the thing that got him back to eating.
We keep our paws crossed for Fern.