They are most likely hatchery birds, then. At least my feed store orders from Ideal Hatchery. I asked that because internal laying and ovarian cancer are fairly common in hatchery birds, though usually death occurs more around 3 or 4 years, I believe. An occasional sneeze is probably just dustiness or similar, not respiratory. Be sure they are getting enough caclium, at least on layer feed, and possibly oyster shell on the side, as some birds seem to need more calcium than even layer provides. You can give a calcium boost with a Tums in the water now and then, or a human calcium pill. One possible cause of death is eggbound, and one of the approaches with an eggbound hen is giving calcium. I don't know what the "embryo" was, of course, though it does sound like it could be a malformed egg. It is also possible it was part of her reproductive tract.
I didn't think to ask about lice/mites. Any of these parasites can kill them if the infestation is heavy enough. You can see lice/mites if you know what to look for and check at night, as some are only on them at night.
I would try worming them, myself. I worm once or twice a year with Valbazen. You could also get a fecal for worms done at your vet; even vets who won't see chickens will often do this test, and it is not expensive. I don't know what happened to your hen, but worms are fairly common, particularly when the soil is warm, as at this time of year, and if it tends to be moist. The first time I wormed my hens, their feed consumption went down, and yet they gained some weight. I assume the worms were eating more feed than they were.
https://www.backyardchickens.com/t/...ll-seeing-live-worms-in-poo/0_20#post_9315842
http://healthybirds.umd.edu/Disease/Deworming Birds.pdf
http://ohioline.osu.edu/vme-fact/0018.html
Good luck!
. What sickness did this chicken have? Is it contagious? What should I do? If you have any questions I will be willing to answer. Thank you for your help.
