burgandyrae
In the Brooder
I would suspect malnourishment or egg yolk peritonitis. She needs to be picked up, cleaned up, weighed, fed the best you can feed her, and a trip to the vet if at all possible would be good.
Ducks can recover from EYP, but it is not guaranteed. If that's what it is, she needs antibiotics, something like Baytril, and may need to be syringe or tube fed. That is not impossible, @casportpony
has published information on it (look up "team tube feeding").
What is EYP?