Your hen looks nearly as flat as a pancake in that photo! That's quite a recovery.
I wouldn't be surprised if she ingested mold with the wet weather we've had here. I've tried to keep their food fresh and dishes cleaned out, but some of the pullets like to throw it on the ground and the others peck at it even after it's soggy. The run will likely get deep mulching or sand come spring to help mitigate future moisture issues.
She rests with her eyes closed, but will open them. Only one is sort of swollen, but that's the side she's best resting her face to the towels and rubbing most.
Tonight has been a bit more restless - stretching her legs higher so she ends up practically standing on her head. If she wasn't in a sling she would cartwheel for sure. She's chirped a few times today like she's mad her body won't cooperate. But the spasms don't last as long.
This is a video from just now - she has moments where she can hold herself up and looks around, but with her neck still bent. (The link should work, I realized the settings were wrong on the video)
Would charcoal do anything at this point, or is it just a waiting game to see if she improves?