Hi Happima, first I want to thank you for keeping us informed on how your hen is doing. Sometimes it seems like no one is watching b/c you don't get replies. Maybe that's because no one has a good answer - you are right- this disease stuff is the hardest part and you've had more than your share of bad luck here. And yes, vets are expensive. That's why we try our best to help each other, but sometimes you just need to get a diagnosis.
I do want to mention on treating all of them - this is what I would do. Of course its just my opinion based on my experience someone else may say different. I've had undiagnosed respiratory disease in my flock. I had no idea what it was. I treated with same stuff you are using and treated one by one and ended up just chasing it in circles with some birds getting it more than once. Eventually, I had to treat all of them at the same time to get rid of it. So since you have the obviously ill bird separated, I'd keep her separated through the course of treatment. I would not treat the other birds unless one of them comes down with it and the reasoning there is the bug can build resistance to the medication if you indescrimately treat. But if any one of them comes down with it, then I would go ahead and treat all, since they all would have been exposed. You should know before long how to proceed - just a matter of days if they show symptoms or not. Please keep posting on how you're doing. We all learn that way.
One more thing - right after you finish the treatment, be sure to give them the probiotics to help their internal good bacteria build back up.
I do want to mention on treating all of them - this is what I would do. Of course its just my opinion based on my experience someone else may say different. I've had undiagnosed respiratory disease in my flock. I had no idea what it was. I treated with same stuff you are using and treated one by one and ended up just chasing it in circles with some birds getting it more than once. Eventually, I had to treat all of them at the same time to get rid of it. So since you have the obviously ill bird separated, I'd keep her separated through the course of treatment. I would not treat the other birds unless one of them comes down with it and the reasoning there is the bug can build resistance to the medication if you indescrimately treat. But if any one of them comes down with it, then I would go ahead and treat all, since they all would have been exposed. You should know before long how to proceed - just a matter of days if they show symptoms or not. Please keep posting on how you're doing. We all learn that way.
One more thing - right after you finish the treatment, be sure to give them the probiotics to help their internal good bacteria build back up.