So a five-month-old pullet is walking around like a normal chicken, eating like a normal chicken, acting like a normal chicken, except she sounds like a goose that wandered into the wrong barnyard. That's the kind of problem that makes you question everything you thought you knew about poultry. I get it. You've done the responsible things: separated her from the flock, took her to a vet, administered Tiagard and whatever RX they prescribed. And still, honk. It's been a month. The poor bird hasn't turned into a waterfowl, but your nerves might be turning into jelly.
Let's talk about what matters most here: her behavior is completely normal. That's your biggest clue. If she were battling a respiratory disease that could sweep through the flock, you'd likely see other signs, droopy wings, sneezing, reduced appetite, lethargy. You're not seeing those. She's eating fine, she's acting fine, she's just… honking. Now, I'm not a vet, and I'm not going to pretend the internet can replace one, but I will tell you this: some chickens develop weird vocalizations as they mature, especially pullets approaching laying age. Their bodies are changing, their hormones are shifting, and sometimes their voice boxes decide to experiment with a new sound. Could be a form of respiratory irritation that isn't progressing into something worse. Could be a minor anatomical quirk. The fact that a month of treatment hasn't changed the sound suggests it might not be a typical infection.
Here's what I would tell a friend who asked me about this, whispered over the fence: keep her isolated for another week or two while monitoring the rest of the flock for any signs of illness. If nobody else starts honking, you're probably dealing with a one-bird mystery, not an epidemic. And if the sound itself bothers you more than her health does, which is a valid feeling, honking is weird, consider whether you can live with a pullet who sounds like she's about to take off for the nearest pond. She might just be that chicken. Not every sound is a disease. Sometimes a chicken is just weird. And in my experience, the weird ones are the most memorable. Keep an eye on her, trust your vet, and don't let a honk convince you that the sky is falling, until you see feathers from above.