Last Thursday (Thanksgiving) my 6 mo. Barred Rock was totally normal. Then she coughed a few times. After that she would "honk" when exhaling. That subsided in 2 days but she still wheezed when breathing. Yesterday (1week from start) her breathing became labored with occasional loud gasping. Today is worse with more gasping. She had been eating scratch before the coughing and ate some California Pepper Tree leaves. There are no other symptoms - no discharge, normal poop, eyes normal. Crop and stomach soft. Ate and drank normal until today. Three other chickens are fine. I gave her some tetracycline this morning. Any ideas??????