If you are able to tend to her, I would probably give her a chance to get better, but also if you choose to cull her eventually to end her suffering, I would get the necropsy done to rule out Mareks. You need to know if the virus is on your property, especially if getting other chickens. You also might want to re-read some of the Mareks links in previous posts,especially the Mareks Fac, and Partners links. Keep us informed about her, and I hope she starts feeling better.