Corid is really not hard on them. Sulfa meds are, which are sometimes used to treat coccidiosis. Vitamins and probiotics are a good idea any time there has been a digestive upset. Glad she passed an egg and is feeling better. Hopefully it doesn't happen like that again.
Collect a mixed sample of several fresh droppings, under the roosts in the morning is usually a good way to get a broad sample. You don't necessarily need to do each individual bird, unless one is sick and you want to specifically check that one. If you are just routinely checking for parasites a broad sample from the flock is good, if one has them then generally you treat the whole flock anyway.