My white Marans died last night. She had labored breathing yesterday morning, worsened as the day wore on. Isolated her and gave her Sulmet. Happened so fast. She had no nasal discharge, no eye problems, no smell. Does this still sound like coryza? Do I need to put Sulmet in the flock waterer? I've never had any sickness problems, keep a clean coop/feeder/waterer. They do free range. Haven't had any new birds since getting chicks in March. What can I do??