Glad you got the results back.
What dosage of Corid did you use? Do you have Liquid or Powdered Corid?
Amprolium is not based on weight, the dosage for all chickens is the same regardless of size, it's added to the drinking water.
Liquid Corid dosage is 2 teaspoons per gallon of water and Powdered Corid is 1 1/2 teaspoons per gallon of water. Give for 5-7 days as the only source of drinking water.
For some strains of Coccidia a sulfa drug would be more effective. Did your vet suggest treating her with another drug? SMZ-TMP may be better to use than Amprolium if you have been treating her with the correct doses.