I have a ameraucana around 5 or six months old who has been sneezing with little bit of clear discharge from nose for about 2 weeks. Stool is normal. She has no other symptoms. The other 3 hens have no symptoms. Recently added some straw to the run. What could this be?
How dusty is the straw? Dust can sometimes irritate chicken respiratory tracts, causing sneezing. But I would think that some of your other birds would be affected if this were the case. It is possible, IMO, that your hen has a mild respiratory disease.
I would isolate her in a warm, clean place and just observe her for a few days. Give her vitamins and possibly probiotics in her water, if possible, and minimize stressing her out. Don't put straw in her isolation area; see if that makes a difference. If it is a respiratory disease, this supportive care may help.
If she gets worse, or you want to try treating her faster, you could get an antibiotic. I would recommend, if possible, getting Tylan50 or Tylan200 (the 200 version is just more concentrated). Preferably, I would get the injectable Tylan form instead of the water soluble form. Oxytetracycline (sold under names like Duramycin, Terramycin, Tetroxy HCA-280, etc.) would be another choice, though it isn't as effective as Tylan. Both antibiotics can generally be found at a livestock supply store, with prices ranging from $9-$15 for Oxytetracycline and $15-$30 for Tylan.
The Tylan50 injectable dosage is 1cc for large-fowl, .5ccs for bantams, injected into one side of the breast once daily for 5 days. The Tylan200 injectable dosage is .5ccs for large-fowl, .1-.3ccs for bantams, injected into one side of the breast once daily for 3-4 days. Alternate the side of the breast that you inject into, and use a small gauge needle, as Tylan can make the injection area sore. In the case of powdered Oxytetracycline (I'm going to abbreviate it OXT), the dosage is 1 teaspoon OXT per gallon of drinking water for 7-14 days. During antibiotic treatment, do not give probiotics, dairy products, or apple cider vinegar.