Hen Painted with swollen vent and diarrhoea

[landferno]

I have a hen painted which I got from a friend a few months ago. I noticed after a few days in the aviary that she had a swollen vent so I put her in a hospital cage and she passed an egg. I've kept her in a small cage since but its been a number of weeks and there appears to be little improvement. I've wormed her, dropped some ivermectin on her neck, treated her for coccidiosis, put apple cider vinegar in the water and even tried a bit of lime juice. I've done this periodically not constantly so she's had time between treatments. She still has a swollen vent, with little feathers around it and is passing a fairly watery dropping although its a bit more solid than it was initially. She's in very good health otherwise with decent plumage and body weight. Any ideas or suggestions on what the issue might be and also any potential remedies?