I think you need to put this duckling on liquid b complex sounds like she is developing a niacin deficiency.
Get her on it asap and she should recover pretty quick
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
This gives info and doses
Get her on it asap and she should recover pretty quick
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
This gives info and doses