I know birds don't show too many outward signs of illness until they get pretty far along - but I didn't expect 'very sick' (that sounds crass - I'm not trying to be : )
Since they free range around the yard I couldn't tell which poop was hers but I'll be sure to pay more attention tomorrow. Its possible the yellow was egg yolk.
They just started laying in August - and all the shells are fine - smooth, hard - I can't tell which one is hers, specifically, but there are no marked differences between the shells, anyway (my inexperienced opinion, of course).
I'll set her up somewhere comfortable tomorrow morning and try to examine her better.
Thank you!