I don't know much about ducks and a family member is sick, so I'm going to try asking @Miss Lydia or @Isaac 0 if they have time to help. I will check back.
Cucumber is good for hydration, though it is a diuretic, so it can make droppings looser. I would try some, but maybe not as a main food.
Soaked chia seeds sound great. I have only given them occasionally, but I would think they would be ok.
Sorry my posting is sporadic. A family member is...
Bsfl are usually a good food to try. I would recommend it.
I would try a little applesauce to see if she likes it. Sometimes they don't.
They sometimes like leafy green vegetables chopped, for fiber and nutrition. They sometimes eat kale when they don't want grass, or vice versa. I try...
Digestive issues are hard on birds. They can recover, if it doesn't become too complicated, but it can be scary. It's important that they keep eating and drinking.
They can't digest milk, so it can make droppings look weird if the yogurt is milk-based. This can sometimes hide improvement...
Ok, that's good. Eating and drinking are good signs.
If you have a 100x microscope, it may be possible to make homemade floatation solution to look for parasite eggs. I have some links on that, somewhere...
If it's starting nearer to her mouth, or she has a partial blockage, this article may help: https://www.backyardchickens.com/articles/how-to-treat-sour-crop-and-impacted-crop-and-how-to-know-which-one-youre-dealing-with.73607/
I understand about the number of birds. I've been there a couple...
I forgot to mention, internal parasites can cause this, as well. Any vet should be able to test her droppings for worm eggs, including dog vets. It shouldn't be expensive. They may not know the best treatment for your flock, but can do the test.
How old is she?
I'm sorry she's sick. Cleaning was good. I usually trim feathers around her vent to make things easier. You can try giving her poultry vitamins/probiotics and calcium. That sometimes helps.
I don't know if you can tell when she last laid. Sometimes this kind of thing can mean an egg is stuck...
I'm sorry you're going through this. I don't have ducks, but have you tried warm baths of Epsom salt or antiseptic? You can also check the ducks subforum at https://www.backyardchickens.com/forums/ducks.42/
It's hard to know what is wrong from the description, but you could try poultry vitamins/probiotics for a boost. Does she have adequate calcium? You can check if her crop is full when she goes to bed, and it should be empty before she gets up.
I believe they can get sick from bullying, but it's...
Thanks! We've had other funny eggs once in a while, such as double-yolked, but this is the first "nested" mini egg I've seen. Thanks for the link! That's a good reference.