I would suggest placing her in an isolation area where you can more closely monitor her. For situations like this I use a small animal cage that I have in the house in an area where the bird can be calm and quiet but is able to be closely monitored and provided the things that she may need such as warmth hydration and nutrition while being protected from flock mates and protecting the flock from further exposure until I'm sure when I'm dealing with.
It would also be helpful if possible for you to take a short video of her prior to putting her in isolation so that we can see what you are seeing.
It will also help us if you include the age breed etc for this bird. Have you made any recent changes to the make up of your flock? Are they can find it all times or able to go ranging which would give her the possibility of being exposed to or ingesting something? What has the flock been fed in the past 24 hours?
That can be a sign of dying or she may have gotten injured. Take her aside, and try to get her drinking some fluids. Poultry NutriDrench or electrolytes would be good for her. Offer some chopped egg with her usual chicken feed. Give her an examine by checking her crop for fullness or puffiness, and emptying by morning. Look for injuries, check her walking for weakness of either wing or leg. Look for mites or lice. If she is laying eggs, feel inside her vent with a finger for a stuck egg. Keep her separated until she is back to normal.