OK, this may sound like a bit of odd advice....but. Pick up Kelly...and smell her breath. Yes....put your nose right up there to her little beak, and give it a good whiff. If it smells sour...say...like sileage..or rotten wet feed...then she has sour crop. IF she has the sour crop, there are a few things you can try.
1. Get some olive oil, ( I used vegetable oil too) Put some in an eye dropper, and drip it along her beak. She will instinctively start "drinking" it. Do this a few times....make sure to get quite a bit in her. Give her about 5 minutes or so...and what I did, was to hold her upside down by her feet...and after she stops flapping around....gently message her crop. This will induce vomiting. Make sure she is upside down, so she doesnt asperate into her lungs.
2. Make a solution of dry oatmeal, and veggie oil..and make sure she is eating it. The oil will help to loosen whats in there, and hopefully pass it.
If you dont smell sour crop...it could be a load of worms. Have you checked her poo? Is it normal...stiff, brown/black and white? Worming her might be the answer.
Also...check her for lice/mites. They will make her very lethargic. Check her vent area, under her wings, and at the back of her head.
I hope she makes a full recovery....keep us posted!