I'm a freak so I'd probably start weighing her on a food scale to make sure she is actually making significant daily gains. A deficiency in niacin can cause stunted growth and unsteadiness to the feet, so you may try supplementing niacin for a few days and see if there is any improvement. Post a picture next time she poops.
Here is some more info regarding niacin deficiency in waterfowl,
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
Here is some more info regarding niacin deficiency in waterfowl,
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/