It worked pretty quick when my 2011 girls had coccidiosis as chicks. Seems like it was overnight with them. :) Just remember to keep dosing for the full period, even after they look like they're cured.
:hugs I'm so sorry, Fishnet. I was rooting for her. Just remember that she had the best life a hen could have after you rescued her, and she died as a beloved pet, not as 'just a chicken'.