It kinda sounds like she is regurgitating water from her crop. I would check her crop daily and make sure she's eating. When I pick up a hen and put light pressure on her crop they will throw up. She might be drinking too much water. It hard to say about the poop, maybe post a picture. Some watery poop is normal. I would continue the medicated feed mix for coccidiosis since its diluted I would feed for another week and slowly ween them back on regular food i.e. do 80%reg and 20% medicated. The warning I give on medicated chick feed is that as long as your chickens are in a environment to pick up cocci so their systems can get develope immunity, you should be fine. I had a friend that had her chicks in a shed on medicated chick feed, then she put the chicks outside with hens when they got old enough and switched them to regular food. They died in 2-3 days because their immune systems were never exposed to cocci while being on medicated feed. The necropsy came back and they died from over load on cocci.
I also had a chick that got neurological from medicated feed because of the binding of thiamine also known as vit b1. I had to give her inj of vit b1 in the thigh for a week. I know it scary, I am just glad I work at a animal hospital so I learned these things. I think in your case you should be okay since you are mixing it half and half. I would also give them 1Tbs of apple cider vinegar per gallon water, make sure they get some kind of grit (u can get at tsc) and u can supplement protein with some calf manna to help her put on weight. You could always separate her and put in a dog/cat crate so you can make sure she is eating. I feed my chickens 17% chick grower mash from hoke mills, supplement with calf manna, grit and oyster shell. I use ACV in their water for a week every month, deworm with wazine 1-2 times a year and cocci with corid 1-2 times a year. This seems to be working for me. I'm sure other people will have some recommendations as well. Good luck!
