Update: SHES EATING HER DUCK FOOD RIGHT NOW!!!!
I took her to the vet yesterday. He drained
300ml of fluid from her. Said that wasn't all but he it could cause really bad dehydration if he took it all. He said it was worth trying antibiotics. She pretty much immediately get some of her bad attitude and curiosity back after the drain.
Inlearned how to force feed pills to a duck yesterday. Took me probably 15 minutes to get the first half of the pill down... I've gotten a bit faster now but Darla's making a bigger effort to not open her mouth ...
Yesterday I found she would eat old fashioned oats so long as they didn't get wet before she dunked them herself in water

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Gave her nutridrench with oats and mealworms last night. She did a tiny bit of preening which she hadn't been doing and her feathers have degraded a lot.
Today since she seemed to be getting her appetite back decided I would make more of an effort to get food in her as it seems like one of her biggest issues has been just weakness. She got three separate meals today of all she could eat oats, mealworms peas with a side of electrolytes.
During bath time I noticed my roen having some behaviors that suggested she needed a bit more grit so I set some out for her. Darla then decided to eat some! Which she wouldn't have before! So I said what the hell might as well try for the millionth time and put some duck chow out and she DOVE into it! I'm so happy. She's Definitely not out of the woods yet. And she might just end up going through this all again if it is some sort of organ failure but seeing her spend a lot more time preening and eating regular food is so good and I'm so glad that neither she nor I gave up.
Thanks for going through this with me. I'll keep updating....
I actually tried to delete this and redo the update.
Almost right after I posted I had put out grit for her friend and she started eating it so I figured "what the hell" and decided I'd try for the 100th time to offer duck chow and she DUG in!!!
She also started preening way more than she had yesterday.
She definitely has been super weak. And with my new feeding schedule for her (3-4 meals of all you can eat peas, oats and mealworms) seemed to give her more energy. I'll keep doing that even though she might be eating her regular food just because I know she needs the calories. But especially yesterday and today she's had a much larger appetite much closer to what it typically is.
I'll try the banana but they've never had it before so they probably will be terrified of it haha I don't want to force feed her more if I don't have too. Neither of us enjoy the experience
Antibiotic is clavamox