Hi. I'm trying to determine what's wrong with my Australorp. She's a little over a year old. A little history of my flock: I got four chicks from the same person in March of 2015. One, a Silkie, was full-grown and the other three were 8-10 weeks old. About 6 months ago, my Silkie stopped eating, wouldn't stand, started having trouble breathing and then died about 72 hours after her symptoms started. I still have no idea what was wrong. About 6 weeks ago, my Australorp was attacked by an owl. She survived but was pretty traumatized. A tiny part of her comb was bit off and she lost some tail feathers. She hasn't laid an egg since. She seemed fine until about 4 days ago. I noticed she seemed "depressed and withdrawn". She also started curling one leg and dragging the foot behind her a bit, like it was injured (it's not). Her "limping" is getting worse and for the past two days, she's been hanging out under the coop and not walking around with the other two chickens. She also feels lighter as if she's lost weight, and I noticed some "bright green poop" in the coop. She has loose stools. This evening, I separated her and brought her inside, giving her her own food and water.
I know it's now too late to keep my other two from being infected if it's Mareks. They seem normal and healthy at this time. What should I do??