Duck stopped eating

[soso143]

Hello everyone, about 3 days ago my 12 week old pekin female stopped eating. She won't eat treats, crumbles with and without water, vegetables, or anything. She is still swimming, preening, and waking around, and drinking like normal. A few days ago she was eating just fine, one morning she just stopped eating. I've given her, water with molasses, and water with electrolytes. She will eat mud though :/ . She isn't pooping, it's 98% water. She will pick up food, but spits most of it out. It hasn't been overly hot, and my other 2 babies are absolutely fine. I checked inside her bill, massaged her gullet in case there was a blockage but it was empty. She does get to free range for a few hours outside their pen everyday, but they all eat the same things so I don't believe she could have eaten anything toxic. Please help, thank you.