The chickens are all between 10 and 12 weeks old. I live in western Washington and the temperatures around this time range from around 50 at night on the low side up to occasionally mid-seventies during the daytime. I am giving them the treatment dosage of the powder for it which I believe is approximately 24%. My plan was to use a bleach and water solution to disinfect the couch after I cleaned out all their shavings and attempt to brush and fan out all the Dust. IMHO at 10-12wks they should not need any additional heat.
Any other symptoms besides labored breathing in the Cochin - sneezing, eye/nasal discharge?
I would make sure she is getting enough Corid.
Cocci can cause lethargy, not eating, diarrhea with mucus or blood, loss of balance, puffed up appearance and distress.
It's always possible that she may have a respiratory illness - I suggest you look at the video link below to see if she is exhibiting Cocci symptoms or respiratory symptoms.
(Corid dosage for Cocci is 1 1/2 teaspoons Corid powder per gallon or 2 teaspoons of 9.6% Corid liquid per gallon
Give for 5-7 days - make sure this is the
ONLY water available during that time period. Mix a fresh batch at least once a day.
https://www.backyardchickens.com/t/818879/updated-corid-and-amprol-amprolium-dosing)
Video - chick with Cocci starts around 1:55 mark:
http://www.easychickenry.com/coccidiosis-in-chickens.html