Lymphoid leucosis is an avian virus, very, very common. It's similar to Marek's but caused by a different virus. If this is what is making your hen sick, likely, the flock you got her from has it. All chickens exposed to it become carriers, although not all carriers of the virus become sick and die. Flock owners with this virus often never realize it's in their flock as only occasional chickens die from it.
Unfortunately, your hen will likely die if this is what she has. The only way to know is to have a necropsy done after she dies. Usually, the identifying feature of leucosis is a grossly enlarged liver. It's easy to spot even by a chicken owner doing their own necropsy.
My flock carries this virus, and when I took the young rooster in for the necropsy that identified the virus, he had a two pound liver.
Your hen will let you know when she wants it to end. She will close her eyes and stop eating, and will not move or be responsive. Or she may still be alert, but will not be able to move or eat.
Unfortunately, your hen will likely die if this is what she has. The only way to know is to have a necropsy done after she dies. Usually, the identifying feature of leucosis is a grossly enlarged liver. It's easy to spot even by a chicken owner doing their own necropsy.
My flock carries this virus, and when I took the young rooster in for the necropsy that identified the virus, he had a two pound liver.
Your hen will let you know when she wants it to end. She will close her eyes and stop eating, and will not move or be responsive. Or she may still be alert, but will not be able to move or eat.