Why for 4 weeks, then for the rest of the summer?
Corid powder dose is 1 1/2tsp per gallon of water given for 5-7 days.
You **can** do a follow-up dosing after skipping a week at a rate of 1/3tsp Corid powder for another 5-7 days.
I would not give Corid long term like you are doing...
What exactly are her symptoms? Coccidia will show up on just about any test, it's in the poop, the intestines and in soil. Only when there is an Overload is Coccidia a problem.
If you have been giving Corid for 4 weeks, then I'd stop it all together.
Give plain fresh water. Fresh feed.
Getting a necropsy on a bird if you lose them will give you answers. I suggest that you spend the money (if there's a fee) on that instead of a vet. With paralysis and losing so many birds, I would suspect that you may be dealing with something like Marek's disease, but the only way to really know is to get a necropsy.
Having the INFO will help you know if what you are dealing with is actually treatable with medications, if you need to make some dietary changes or if you are dealing with disease where you manage symptoms or cull sick birds.
You live in TN right? I believe there is no "fee" for residents when testing is performed on livestock but give them a Call. It's better to Call the labs and talk to a pathologist, often they will work with you on a lot of things. Worth a phone call!
https://www.tn.gov/agriculture/animals/-c--e--kord-animal-health-diagnostic-lab.html