Sounds like stridor which is when they get food/water and/or mucous in the airway.
If her crop is not emptying and its fluid filled she may be aspirating some fluids.
Another possibility is if she's got fluid in the abdomen below the vent between her legs - do you feel any swelling or bloat...
That's a roundworm. The Safeguard will take care of that. I wouldn't use Ivermectin since it seems to have lost some of its effectiveness.
Dose for Safeguard is 0.23ml per pound of weight given orally once daily for 5 days in a row.
If the others a bit droopy, then treating them would be...
I would address the crop symptom and see if you can get it to start emptying. This article will walk you through treatments.
https://www.backyardchickens.com/articles/how-to-treat-sour-crop-and-impacted-crop-and-how-to-know-which-one-youre-dealing-with.73607/
Hold the cup up to her beak and see if she will drink.
If you have a chick water station, try using that when you separate out birds, they seem to recognize that little thing and will drink from it.
Photos of her and the poop may be helpful. There are so many things that affect chickens...
I'm sorry you lost her.
Do you still have the body? If so, refrigerate it and send it to your State Lab for diagnostics you can find out why she died.
Since you have another that is not feeling well, if you lose this one, then definitely send for testing.
Check your feed to make sure...
I would re-check her crop again in the morning, if it's not emptied, then I'd begin treating that symptom according to this article https://www.backyardchickens.com/articles/how-to-treat-sour-crop-and-impacted-crop-and-how-to-know-which-one-youre-dealing-with.73607/
If you are giving a strong...