Keep up corid treatment and treat for the mites/lice as well.
If your chook is feeling sick from coccidiosis, she will be moving less, dustbathing less and preening less. Therefore she will be more susceptible to parasites.
I’m just saying that this is not necessarily an either/or situation, although it could be.
You need to treat your whole flock with a permethrin powder or equivalent. DE in the dust bathing areas works as a preventative, not a cure. You also need to clean out their coop, treat the structure and put new bedding in.
Depending on the severity of the mite/lice infestation and your weather conditions, you will need to retreat at intervals until they are gone.
This is a hands-on job unfortunately. Unless you can source Exzolt fluralaner. That will take care of all ectoparasites.
Is there anyone who can help you?