Coccidiosis is a parasite.... the Corid starves the parasites of essential vitamin b, which starves it. At this point you probably should keep that chicken separate since she’s already started treatment, and now you’re wanting to treat the others. Leave the water and make sure it is their only source of water so they definitely drink it. After they are treated for 5 days, then I would add the separated chicken back to the flock (to avoid overdose, you know what I’m saying)? Normally, you would just treat the whole flock together if you see symptoms from just one bird but since you’ve already separated and started treatment like I said, I would continue with that and treat the rest of the flock so by the time you put the separated chicken back everyone is back to fresh drinking water (preferably with a splash of ACV to hell restore the vitamin b that was starved out.
If you have a small dog crate, I would put her in that directly in the coop / run (making sure it is completely predator proof and protected from elements) with separate food and water so she can still be with them but not drink their medicated water.