Chicken weak and falling over

[Renada_]

She want fine this morning when I let them out and now just four hours later she’s laying on her side and can’t seem to get up. I put her in front of a heater and she can stand a little bit, but still just wants to lay down! She’s about 21 weeks old. She keeps closing her eyes and refusing to move around. It’s was below freezing last night and this morning has also been extremely cold if that helps. She also has feathers that keep falling off and I’m assuming maybe she’s molting? I’ll attach a photo of her bum because she has a bit of wet butt. And a video of how she is acting.

 

[Insnesnakos]

I don't know but it seems like she is sick
Someone with more experience should be able to help you

 

[Eggcessive]

Was she vaccinated for Mareks disease? With her curled under toes on her right foot, and hesitancy to walk, preferring to sit down on her hocks, I would be concerned that it could be Mareks. Be sure to keep her near food and water, and offer those several times a day. Adding water to a small bowl of chicken feed is a way to get more water into her. Chicken sling chairs can help get a lame hen upright, and to help feed them. Here are some examples:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/

 

[Renada_]

Sadly she passed away :/ I’m not sure if she was vaccinated for Mareks, I got her when she was about a week or two old from a chicken farmer out of town. Both of my Wyandottes from there passed away, so I don’t think they were vaccinated. All of the chicks I’ve hatched get vaccinated by me, I think I’ll order Wyandotte hatching eggs in spring instead of buying another.