I have run into plenty of people right here on BYC with adult birds that have been diagnosed with Coccidiosis as adults and been very ill.Sorry Kiki, we will just have to disagree.
I just have never had it happen in all my life. Once they build up an immunity to the "parasites" they are ok, unless they have a challenged immunal system. We have never had an adult cow or pig come down with it again.
As babies, they are extremely vulnerable to these nasty bugs.
The cocci are always in the soil, and if they did not build up an immunity to these bugs, then ALL birds and animals would continually be ill from these bugs.
As they grow and build up immunity, the bugs are all still there, still in their gut, cows, pigs, birds, all still there, their guts full of the bugs. but the bugs can no longer harm them as their immunity has been built.
Calves and pigs are extremely susceptible to cocci also.
If it were me, I'd worm her well, repeat in 10 days.
In fact, the whole flock should be wormed.
I worm all my birds in spring and in fall. I also use different kinds of wormer, rather than have the nasty bugs build up an immunity to the wormer used. We feed pumpkins to our farm animals and birds, and that alone has shown dead worms on the poop trays in the morning. Pumpkin seeds ! Blew my mind ! But they work !
The only other time I have seen blue combs, is with MG, where the bird just isn't getting enough Oxygen, which is called Cyanosis.
Low red blood cells, Low functioning air sac (or infected), or a bad heart, can cause this.