We're having the same wait with our rescue cat Arwyn. He's been off his food, sickness/diarrhoea and very lethargic for the past few days, so yesterday after an antibiotic injection on Monday did nothing, he ended up staying in at the vets so they can do x-rays, blood tests and so on. I have to ring at 2 if I've heard nothing by then.
The vet was still hopeful last night that it''s just an infection, or something he's eaten, but you can't help but start to think of worse possibilities.
I hope the vet gets to the bottom of what's causing Delphi to be ill and that she makes a speedy recovery.