Pigeon-toed, injured, or Marek's?

[grammaC]

My Welsummer hen is about 4 1/2 months old. Was vaccinated at hatchery. Grew up fine with flock mates. Suddenly, she is pigeon-toed, injured or has Marek's disease. She can't walk without stepping on her own feet, losing her balance and tipping forward or sideways. She uses her wing to balance and sits on her hocks. Needless to say, she doesn't go anywhere if she can help it, but will eat and drink and poop if I bring the food to her. It started about four days ago. So far, no other chickens are affected. Her feet are free from bumblefoot and her leg and toe joints all seem to work fine. No hotness around any joints.

Adding photos to help explain. Can I splint her legs or something to correct this? Is it Marek's?
Thanks..

 

[azygous]

She's too old to try to intervene with orthopedic measures.

When did this come on? Has she always been like this? It does look like an avian virus. Only a necropsy can identify what disease may be present, and the chicken has to die for that.