Hen with labored breathing...how to treat?

[BayFillyZ]

I have a 2 year old cochin hen who has had labored breathing and a periodic "honking" sound as she breaths for the last 3 weeks. I need help diagnosing what is wrong so I will know how to treat for it. So far I have been swabbing her beak throat and underwing with Vet Rx but the breathing issue persists. She does not seem to have any other symptoms. She is eating and active. No sneezing or visible discharge from her beak or eyes. Bronchitis? Pneumonia? I have been closing the chickens up in their house at night because of the colder weather. Even though its ventilated and I clean it daily I wonder if her symptoms are the result of ammonia overdose ?
Thanks!

 

[Eggcessive]

If she has no nasal drainage I would think she is having a problem with dust or something in the coop. Aspergillosis can also cause a change in the voice. It is a fungus from mold. Here is a link: http://msucares.com/poultry/diseases/disfungi.htm