Is it hot there? Have you taken measures to keep them all cool?
Does she have any runny nose? If so, swipe it with your finger and smell it. If it smells bad, it's choryza. I had a girl get it, and isolated and treated with an antibiotic and she got well! You'll need to look up to see which antibiotic is appropriate. I keep Tylan inj. on hand all the time.
The noisy breathing: is it in her throat or her chest? Did you put her chest to your ear? Yeah, it looks odd, but I did this a lot when diagnosing my birds. Seal her chest agains your ear and you'll hear the rales if they are there. Very fine sounds, like if you took your hair between your fingers and held it near your ear and rubbed the hairs against each other between your thumb and forefinger.
Is she coughing and wheezing? I had a girl get infectious laryngotracheitis and choke to death right in front of me. Totally helpless to fix her. The state necropsy lab said she didn't have it, but I'm not so sure. It's very contagious, but no one else got sick.
Plain yogurt! Always, yogurt.