Hi
No I was suggesting foods high in selenium rather than giving it as a supplement. Seafood, fish, wholemeal bread, sunflower seeds and eggs... these all contain above average levels of it I believe and are things that a chicken will probably enjoy eating.
I tried turmeric and black pepper...
As someone who has Marek's in their flock I can say that unfortunately that does look like it could be. She is at an age when she is quite susceptible and it is a very widespread and easily contracted virus. I've certainly had birds with nice red combs that were bright eyed and voracious eaters...