My vet did say Hannah seems to be very sensitive when after xray, checking bacteria in her poop etc didn't lead us to any specific issue. Basic bloodwork done showed her as being anemic, but that's as far as we went. He said I should change to Mazuri duck food, but I'd have to order it online.It's why duck people are so dedicated. When things go wrong, it can take a lot to figure it out.
It's also possible they had genetic issues. A very long shot. But didn't they come from the same place?