The best thing you can do as a preventative for your flock is good husbandry. As long as they have a good diet and a clean living environment, their immune systems should be able to handle it.
A couple things you can do to boost their immune systems is adding apple cider vinegar to their water and providing fermented feed. The fermented feed has probiotics that will outcompete the coccidian.
Also, when she got antibiotics for the bumblefoot, it would have killed off a lot of the good bacteria in her gut and caused some loose droppings, and a perfect environment for the cocci to take over. Best thing would be to get her gut repopulated with good bacteria...
How do you get fermented feed?