hanging neck

[lovin my duck]

We had 4 ducks, something killed 2 and injured the other 2. I went to the vet and got medicine for them used it and they were doing really good. Now, one of them walks around with her head hung down but will occasionly raise it.she really can't walk that well but her feet are fine, and she is breathing really heavy. Now, I don't have enough money for a vet visit at this time so I want to know if anyone has an idea of what I can try to do? She also, is developing green dots on her bill. They are approximately 6months old.