I am so sorry to hear about your loss. Stay with the corid, I do suspect its cocci. There is hope for the remaining birds if they drink. Eye dropper to get that fluid down but be sure to get past the tongue orifice so they don't aspirate. Don't over treat without seeing other symptoms it may weaken the bird more. Coccidia works fast, but may have a different effect on each bird that gets it. Some just fail faster than others.
Ok thanks, I am just afraid I am going to wake up tomorrow and she will be gone. I was hoping they had a chance since I started the Corid. This is my first big problem with my chickens and its breaking my heart.