I agree with Wynette. It is very likely that something else is bothering her. I'm glad that you separated her. I think i would be feeding her boiled egg yolks (easily absorbed nutrition) and keeping her in a dark quiet area.
If she continues to eat and poop normally, o.k., but if her poops turn runny, i would strongly suspect something wrong in the egg-making department and give her a warm shallow bath to see if she gets 'loosened up.'
Those are just a couple of ideas. I'm no expert, but i think that cocci is very unlikely, and like you said, sitting away from the others puffed up and whatnot, is really just a sign that they 'don't feel good.' At that age, that's really all it's a sign of, i think. When they're babies, cocci is simply the most likely problem. You mentioned that the temps aren't optimum for worms. The cold temperatures aren't conducive to cocci life either.
I know you didn't ask for advice on what's wrong with her, and you have to do what you think is best.
I would keep an eye on that crop - or a finger, actually - i had a cockerel who acted a lot like your'e describing. And he had gotten very skinny. At first his crop seemed fine, but i felt one tiny little bulge at the bottom. I massaged his crop maybe twice, two days in a row, and he was back to normal and immediately started gaining weight.
I said all that to say, keep looking and watching her to see what's wrong.
I hope all goes well.