When I see a broody get out her fry-pan and cook the meat and insects that she has caught for her chicks.... that's when I'll start cooking meat for my birds
Seriously, though, it sounds like you've given them some meat which is a good thing.
I'm wondering if there may have been some kind of predator that could have gotten into the pen at all?
Sometimes mice and rats will attack birds at night when they're on the roost. I know one gal who said she went out at night and could see mice crawling on her birds!!
They will literally pull feathers, etc. if there is an infestation.
I don't remember if you said you saw the other chickens actually attacking her or not.