I'm so sorry that she has not improved. Rather than repeat what has already been said, I'm going to give you this link, for now or future reference. This is how I do it, very quick, very humane, but it's not totally hands off. It's pretty fool proof as long as your loppers are sharp (mine are dedicated to this purpose only). You (or whomever you have do it) can walk away after if necessary, come back later. I've tried several methods, this one works best for me. Unless there is a vet who is willing and affordable, we all have to have some comfortable way to do this at some point. It is never easy.
https://www.muranochickenfarm.com/2017/06/the-easiest-way-to-cull-chicken.html
https://www.muranochickenfarm.com/2017/06/the-easiest-way-to-cull-chicken.html