For what it's worth, B vitamins have helped many ducklings with neurological development - so perhaps adding some brewer's yeast or Super B Complex to her food may boost her a bit. Glad you were able to get a vet's help.
Wow.
Agreed - most likely egg bound, extra calcium, long baths in lukewarm water (no soap), perhaps a little KY jelly on the vent but be careful not to break anything.
You may also want to keep her and her friend in the dark - that slows the egg production system.
Keep her quiet, make sure she...