If it was botulism, she might be dead by now. It moves very quickly to the respiratory system.. There is a treatment, but it's quite harsh and you'd want to be sure that it was botulism before giving it. IT's one of those "She's going to die for sure if I don't" treatments that I leave as a last ditch effort. She's not at that point yet. But I'm so glad that this was brought up because so few people realize this is an issue. It's also a problem where people have compost piles, decaying vegetation, and in any case where maggots might have been consumed.
In the mean time, it's time to rule stuff out as you boost her up.
Can you rule out mites/parasites? There seem to be a bloom of them lately (probably from wild birds) and they can take a bird down like this very quickly. Check the bird carefully, particularly in the warm, moist area around the vent. They're nearly microscopic, and sometimes you just find their eggs. Looking while the bird is on a white sheet helps some people say.
Also, there are issues of heat and a lack of nutrition lately. She's been eating - that's apparent because of her crop. But has her crop emptied? Or is it statis? Check her crop throughout the day to make sure it empties within 24 hours. Checking them first thing in the morning before they even wake up is a good time. Their crop should be empty then. If it's not, let us know.
Also let us know about her droppings. Are they full of clear water? Are they high in urates (white)? Are they normal solid greenish tan with a white urate topping? Or otherwise?
What are your birds eating exactly? Do they have access to grit, and have they recently been allowed access to fresh grass and or greens? Are you on city or well water?
If you use electrolytes, because of the amount of water that birds are drinking in this heat, I'd recommend 1/4th the package dosage. Or you can use apple cider vinegar (organic, not because of the philosophy but because of its mode of manufacture and ingredients) at a rate of 1/2 ounce per gallon in the summer when water consumption is high.
I'd definitely make sure she gets some of what I call "high-nutrition" into her. That would be egg yolk with some water and yogurt mixed in, just 1/4 teaspoon of yogurt. Feed her only easily dissolved foods until a static crop is ruled out by finding her crop empty. That means something that would fall apart in water: pellets/crumbles, egg yolk, etc. No grains until further notice.
I'd also go around and try to eliminate any puddles that you can. I know that's rough. My chickens prefer a good mud puddle to nice fresh clean water. Go figure. See if she's been drinking that.
One more thing - you say she seemed to respond after vitamin therapy. I would personally not recommend packaged vitamins in this case. I'd consider the baby-vitamin recommended often here (the one without iron please). Or I would consider wheat germ oil. You can buy capsules from the grocery store's vitamin section, and they're high in A, D, and E. If she's having issues with vitamin E deficiency (which causes neurological issues), then it'll help. E also helps overall health with its antioxidant activity, and A is helpful for respiratory care in the mean time. I'd use part of one capsule every other day. Mix it in her treat if she'll eat the treat.
Definitely try to get a probiotic down here until something digestive is ruled out by the way.
