"Bubbly" eye not responding to Tylan50

[ValeriePM]

We bought 15 chicks in mid-March that we raised in a brooder. A salmon faverolle had a bubbly eye on and off since we got her but none of the other chicks ever showed symptoms. I washed her eye out and it would subside for days or longer. Now that they are outside, I heard her sneeze the other day so started her on 1/4 cc (only 2.5 months old) of Tylan50 injectable for 5 days. No symptoms during treatment and none of the coop mates have shown any symptoms. Yesterday was day 6 so no Tylan50 and this am her eye is bubbly again. What next?

 

[Eggcessive]

She may not be sick at all, or she could have a virus which will run it's course over a period of weeks. Chickens sneeze occasionally from dust in feed or bedding, so if the sneezing is not frequent, it may be irritation, Coincidentially, I have a salmon faverolles hen who has foamy eyes occasionally during cold weather. It can be foamy in morning, then clear by afternoon. She has feathers around her face, so I'm now convinced it is irritation or a tear duct problem. When first seeing it, I gave some Tylan orally, and there was no change. Then I noticed it came and went, and she had no other symptoms. I've never had MG or mycoplasma in my flock, so whatever it is just just affecting her.