Chicken respiratory distress

There is something wrong with my bantam chicken and I'm not sure what it is. She has laboured breathing, her feet feel hot, she staggers when she walks, she is very fatigued and doesn't stand for long periods. She still eats and drinks normally. I have ruled out mycoplasma as she isn't sneezing and no bubbles in her eyes, she doesn't have coccidiosis (she lays down, which I've not noticed in other chickens even they've had it) and there is no evidence of water belly. My initial diagnosis I came up with, was distress from heat/humidity cause we've had frequent days of high humidity (more than 90%, and temperatures in the low to mid 30s (Celsius) I've had her inside in air conditioning for 2 days now with no change. I also thought she might have botulism which I've also had before but I've not had enough experience with either of these to make a diagnosis I have also noted below a few other things that I've done/observed in the last few weeks. *She and the rest of the flock have been treated with ivermectin 3 weeks ago * she isn't egg bound, she laid an egg yesterday *She doesn't have sour crop, ive smelt her beak, and there is no impaction either *She is the only one out of 18 other chickens displaying these symptoms Please help me

Hello- Lets start with the symptoms:  laboured breathing, hot feet, staggering, unable to stand for long.  There are unfortunately a wide range of disease that can cause these signs.  The first that came to my mind were dilated cardiomyopathy (heart failure) and arthritis, but other possibilities may include avian osteoporosis, gout, various other dietary / nutrition imbalaces, parasites and fungi e.g. gapeworm, mites in the air-sac, aspergillosis; crop impactions as you mentioned and Marek's disease.   However, there are a whole host of others.

The trouble with this approach is that symptoms are only quite rarely indicative of a particular disease; although I can suggest possibilities, I cannot narrow it down for you.  Infectious and nutritional diseases do not look the same every time and in every chicken, so I would be hesitant to rule out any disease on the basis of having seen it presenting differently on a previous occasion, or because all of the signs were not present.   The fact that one one individual is affected, may make infectious diseases and / or nutrition related diseases less likely.  However, it could be that some chickens in the group may be immune to a particular disease or vaccinated, or it could be that one individual's particualar absorption of, or access to, a nutrient may be restricted.  Therefore, it sounds as though a vet who can see this chicken in context would be a good idea.  Please will you let us know if you find out?