Help! Sick chick!
If by chance she did have coccidiosis and she's not drinking then she's not getting enough of the medication to make a difference. You have to give the medicated water with an eye dropper or small, needless syringe every couple hours, or as often as you can during the day, until they feel better and start drinking well on their own. When you treat with Corid it's better not to add anything else to the water until the course of treatment is finished. Then you can add vitamins or probiotics if desired.
This chick may have something else going on however and just may not thrive no matter what you do. Have you tried feeding her some mashed up hard boiled egg?