Treating her will just as likely kill her as the parasites themselves at this point. That parasite dust is tough stuff and if she is at a point that ants are all over her and she isn't even twitching...then I'm so sorry but it is just too late.
For humane animal treatment sake, I would find someone to "put her out of her misery" That has to be just awful and no way for a beloved pet to die. I would immediately isolate the other one and start treating but understand that you have to treat the coop, bedding, run and outside area AND the other chickens as these parasites are host specific the survivors will run and find the next chicken.