She's about 16 days old now? And this has been going on for ?
If you aren't seeing mucous or any obstruction in her beak, no leaking air sac, I'm not sure what else you can do except to see if this resolves on it's own.
Is she staying warm enough? She's got grit right?
How are you able to see the esophagus without seeing the tracheal opening?
Photo reference
https://www.backyardchickens.com/articles/safely-administering-oral-medications-to-all-poultry-and-waterfowl.73335/