I'm going to say she's a chronic soft shelled layer. I have her isolated on and off. Gave her feed mixed with oyster shell (prior I had none out) and Tumbs crushed and desolved in her water. A few days later I got a fairly normal egg. But she's just not thriving. Slower than the others when I walk them back to the coop, easy to pick up unlike every other duck. The soft shells I have recovered were srheads of membrane caked in a powder that should have been shell. She's also a favourite of one drake, I don't know if that's playing into this. Any way no eggs sense the that decent one. Wondering if she's laying internally or has some remnants of those soft egg lodged inside. She is thin, and breathing heavy when active... just my thoughts and observations and what I've done for her so far