When I can get back to my laptop I will send a photo of my baby Runners. Dog kibble if wetted to cooked oatmeal consistency, mashed into tiny bits, with water - we don't want choking!
Glad you are paying close attention!
A good duck vet is always best, but not always an option.
Elfie was slow - took her nearly a year to catch up with everyone else. She sounds similar to your Stella.
But Stella may have something more serious going on. I might put a teaspoon of food...