She just passed away while I was holding her.
Is there any way to treat with Corid and a broad spectrum antibiotic? Does this sound like something an antibiotic would help with? The other 4 bantam girls in her flock seem fine (not that it's going to prevent me from being proactive in treating them from whatever it could be)
I'm so, so sorry 
Are the others eating/drinking/pooping = all normal? If so, then I would probably treat with the Corid, but I wouldn't give antibiotics prophylactically.
You may want to consider sending the body to the state lab for necropsy/testing, to find out the cause. Probably Raleigh or Monroe are the 2 closest labs to you (NC has 4).
http://www.ncagr.gov/vet/ncvdl/
. Hopefully no one else will get sick. Do you know the dosage for treating, and or preventing coccidiosis with corid?