I have not had direct experience with Botulism, perhaps someone else here has and can better direct you than I can. From what I understand, only time and passing the toxins from her body will heal her. If she is doing poorly and not eating or drinking, especially drinking, she may need supportive care. At this point perhaps you can bring her indoors or somewhere you can monitor her closely, and keep her in some sort of confinement very close to food and water.
If she will not eat or drink on her own, her only hope for survival is if you are willing to tube or force feed (tube feeding is actually safer). Placing water or liquid food into her beak can cause her to aspirate and can suffocate her or cause pneumonia. Tubing is putting liquid food directly into the crop so that she cannot choke.
If it is Marek's, there is a good chance she will not survive if she is at the point where she cannot walk AND she is disinterested in feeding herself. Some birds do come back and live for a while longer before passing away, but usually when they get to this point they have aggressive lymphomas.
If you want to try to support her to see if she will survive, again, your option is to tube feed... It will help keep her hydrated and keep the nourishment flowing. If she does have visceral Marek's, though, the cancer will eventually start to shut her organs down even with the tube feeding, so it is not a cure... it is just supportive care in case she does not have the lymphomas.
Some tube feeding links, in case you want to try:
https://www.backyardchickens.com/t/...h-my-bird-pics-for-visuals-very-detailed-post
https://www.backyardchickens.com/t/805728/go-team-tube-feeding
Just as a thought-- this isn't likely but I have to ask, have you checked your feed for mold? Look for 'clumps' of feed or any discoloration or unusual odor (might smell musty, might not). Again I am not experienced enough to offer good advice here, but if you find mold it is something to consider, as many mold toxins can cause neurological distress in birds.
If you lose her, do you have any diagnostics labs for agriculture/poultry, or vets, etc, that you can send her for analysis and necropsy? It might afford you some answers so that you know what to do for the rest of your birds, long-term.