Until you definitively diagnose the problem, there's no way to know which treatment to use. If you have a vet who's willing to see a chicken, that's probably where you should head. Too many different medications will make her sick, if not dead. Caramel coloured poo is not a sign of cocci. This has been going on long enough that there should be blood in the feces. Without isolating her, you won't be able to observe her and her droppings well enough to make a correct diagnosis. If the problem is bacterial or viral, some of the others should be showing symptoms. The sick hen would also have some other symptoms, some of which may be quite subtle. If listlessness and the possibility of weird poo are the only symptoms, it's almost certainly parasites. Wazine only treats a very limited number of roundworm species. I don't even keep it around for that reason. I'd rather use a broad spectrum wormer like Eprinex. Ivomec is also good, but you have to be careful, it can be lethal, even in small doses. Neither Eprinex or Ivomec is approved for use in chickens and Wazine's approval is endangered. The harsh reality is that there isn't much research done on chicken medications. Most sources suggest culling at the first sign of illness. Because we are all weirdos who are emotionally attached to mere chickens, we have to go the extra mile researchers won't in order to diagnose and treat our animals. A vet who is willing to see a chicken is a rarity. If you have access to one, by all means take advantage of it.