As far as I am aware Cocci is mainly a disease of kids, especially if kept indoors. I have just had two of my younger kids having a couple of cycles of Cocci with the slightly older female kids in the neighbouring pen NOT showing any signs of the disease. The initial disease was probably caused by overeating on green stuff, causing diarrhoea, causing illnes and stress, then developing into cocci (as it returned about a week later).
It all depends on previous exposure, and if exposure is sudden or under stress, when the animal cannot cope then disease occurs. If your adult girl had cocci it would be as a result of some stress possibly coupled with some digestive upset and/or worm burden. It will a) be difficult to establish for sure that that was it, as all goats shed the oocysts, and some can have a large burden without any signs of disease. b) treating with an anticocci medicine will deal with it in the meantime.
I have treated my kids with Intradine, which is an injectable drug and therefore can be dosed very well. Your vet may have to order that in especially, as it is not anymore specifically licensed for cocci. I have also used that very successful in lambs (not this year)
If you have cocci in your shed it may be worth to do a serious clean-out before kidding next year, and then keep it freshly strawed and clean for the first few weeks. I don't think that treating the adults prior to kidding as a prophylactic measure is necessary, as kids will need to be exposed to cocci in order to build up immunity. Only when mixing kids/lambs of different ages and the younger ones do not yet have the immunity will coccidiosis happen (or they encounter some unexpected stress factors).
According to my vet book, only one of the 12 cocci causing species is transmissable between sheep and goats, all others are goat specific, it is not transmitted to poultry, pets or others. Therefore treating all your livestock is not necessary. I would also not treat the rest of the goats unless they show any signs. Because they should be able to cope!