I find barley the best for sprouting, it's cheap and mixed grain sprouts at different times leaving it more inclined to rot. Feed stores should have full grain untreated barley, if not Newmarket horse dealers will. Wheat and triticale would be my next choice.
Adult birds aren't usually effected by cocci as they have usually built immunity with their age. Green poop usually means starvation. I would isolate her and monitor her feed intake.
The head hunching sounds more like trying to clear her crop. Examine her, look in her beak for any obstructions and smell her breath.
I should have asked, was there any traces of blood in that poop ?
There was no blood in the poop. I had her on my lap yesterday and her breath didn't smell, but I didn't look in her beak. She's actually looking a bit better this morning. She was in the run when I got up to let them out to free-range. The others charged out. Stampy went into the coop & contemplated the jump to the bottom stable door for ages and then managed it. She's not hunching this morning & was at the bowl with all the others when I gave them their feed soaked in hot water. I'll have another look at her this morning. I did spot a green poop under the roost & am clearing that out each morning as it's the easiest way to keep an eye on the poop spectrum. I really need a little isolation coop. Hmm...