A few other nutritional/supplemental suggestions for respiratory issues before you medicate:
Keep up the yogurt and OACV. Try giving her some poly-vi-sol baby vitamins daily (the kind without iron) or nutri=drench for poultry. Also, I have read Cod liver oil mixed with a hard boiled egg will help boost their immune systems. Somehow, lack of vitamin A can result in respiratory disorders.
I LOVE a product called VetRX. They make one just for poultry, and my local feed store sells it. It is like Vicks vapor rub for chickens. You can mix a tiny bit of it with a drop of hot water, saturate a q tip with it and press it on their nostrils, around their eyes, and then rub some on your hands and apply under their wings or wherever they lay their heads when they sleep. I always do this after they have gone to roost for the night.
I almost always try everything I can to boost their immune systems and speed healing before I medicate.
Be warned though, lots of the issues that cause respiratory distress are not curable, and will re occur and spread through a flock. Some people choose to cull. I don't, and so when the weather changes and I start to hear a little sneeze or raspy voice I immediatly start going with the immune system boosting approach. So far. so good. I have the medications, and if my girls ever start to show advanced symptoms, I'll use them.
Good luck!