Thank you soooo much. I will discard her eggs if the calcium tablet works. . I thought being free ranged in my yard would cover many sins. Like, I would not be completely depending on store food for their health. they Are NEVER in their run. All summer they ate my vegetable garden, fallen peaches, Japanese beetles, and always had a pan of pellets and cracked corn and worms.Some older chickens can still have coccidiosis, especially if weakened or having immunity problems. A fecal float by a vet could rule it out, along with worms. Her poop looks suspicious, so the Corid is probably not a problem. Since she has been laying soft eggs all of her laying time, it may be another problem with her oviduct, but I would give the calcium (calcium with D3) for several days to see if it makes a difference. If not, then discontinue it if she is eating layer.
I do agree that chickens should not eat layer feed until about 20 weeks or when they start to lay. An alternative is to feed all flock/flock raiser feed with a separate container of crushed oyster shell available. I would also discard any of her eggs for a month after treatment with doxy. I think most other tetracyclines will remain in eggs for 21 days.