What are your plans for limpy? As well as your other ducks?
Are they meant for pets and eggs?
Most likely her general appearance has to do with her lack of proper muscles due to not walking like the others. And, a lack of preening.
Was she always smaller?
Could be neurological and it wasn't as noticeable until she got older. Also, since they mostly forage and don't eat commercial feed, she might not be as good at that so is hungry and when she is offered feed she is ravenous. Most domestic ducks are not as good at foraging as their wild counterparts. Plus wild birds are not confined to one area - they can move from place to place to find what they need. Maybe your others are just better at foraging than limpy is.
I would continue with the vitamins especially the b complex if you are wanting to see improvement. Maybe wait a week or two since you just started with the b complex and decide what to do then unless she gets worse in the meantime.
I would also keep the commercial feed available to all ducks - a very little amount so that it doesn't spoil (If they aren't eating it). At least they can choose to eat it or not.
Other than that, I really have no other suggestions.
I wish you and Limpy the best! Hope to see improvement!
Thank you very much for your good wishes, they seem to work! - See below…
Well, since we moved to WV in March this year my wife always wanted to have Chickens for eggs. I was more into planting fruit-trees and -shrubs, work once, harvest for years… And from my childhood experience i do not like chickens, too noisy, stinky, bah!
Then came that day in the local store when my wife found six larger, terribly sweet looking ducklings and the salesclerk told us what would happen to them if they would not find a home soon…


So we bought them immediately, together with two bags of food, a chicken house, feeder, waterer,… And they turned out to be soooo cuuuuute!
So now they are our pets that hopefully start making breakfast for us soon. My wife told me that duck-eggs are much tastier than chicken eggs. All i know is that i don't like goose-eggs - too much white, too little yolk; And i loved to eat the eggs of the »dwarf-chickens« (i think they're called bantams here) almost all yolk, very little white.
I am planning to have more duckies, ordering some from Meyer and fence in more and more of my land so they can forage and do duck things the whole day in exchange for being cute and funny and laying eggs. So for now pets with benefits!