I’m sorry for your loss, and it was a mistake, mistakes happen. I have had chickens for almost 6 years and would have never thought putting a chicken too far forward would mean any harm. The good part about this, is that you have posted it on BYC where lots of people with chickens are on. This way you are teaching others that putting a chicken too far forward can cause harm. The reason she was feeling sick was because she seemed to have pasty butt. Lots of chickens get it it’s when the poop gets stuck in there butt feathers. A way to fix it is to just give her/him a warm bath, or take a wash cloth with warm water and rub it gently until it is gone.