Possible sick chicken

My daughter went to let the chickens out this morning and she shared that one of the chickens was not acting right She shared that when she let them out they got out of the coop. When trying to herd them back in this one red sexling could not walk back innto the coop. It stumbled while going into the coop and it even fell while trying to go up a step. When I saw the chicken she was almost twitching with her head kind of tucked in. She is lethargic and closing her eyes kind of hiding her head under her wing. We brought her in right now till we get some answers. Her poop is runny. She does not seem to have any obvious wounds...HELP...