Amoxicillin is perfect. Give her 250mg right now. Waking her up could keep her from being dead tomorrow. She should have 250mg twice a day. So in the morning, give her the second dose and tomorrow evening give her another. Continue until she's had the antibiotic for at least seven days.
You should notice a dramatic improvement in 24 hours if we're right about the Clostridium perfringens. But keep up with the antibiotic for seven days, ten if she still seems still a bit off.
You should have pushed a calcium into her by now. Give it to her if you haven't. Egg binding can kill, too. If an egg appears, and the hen is suddenly back to her normal self, then we can assume it was egg binding and not the bacterial infection, but give her the amoxy anyway for seven days. It will be cover in case egg binding caused the start of an infection in her reproductive system.
To sum up, you're treating for two possible things. If we're wrong about one and right about the other, no harm done. At least we've got the two most obvious things covered, and you're hen should be back to her self in a week.