This hen is 1.5 years old Bovans Brown, about 6 months ago she developed an irratated red patch on her underside with no feathers. About 3 months ago she was placed in isolation because we suspected it was caused by the other hens picking on her, although the skin never appeared broken. Also started dusting the birds and their area. Today, it's red with just stubs of feathers sprouting, and a week ago she stopped being able standup, and now waddles around without getting her body off the ground. Her tail also appears to be drooping. She is still laying eggs on a daily basis, and all appears normal with them. Examining her, unable to find any other issues that appear to cause it. I'm guessing Marek's disease; any thoughts? See the photos and video below and let me know what you think.