Hello, this is my first year raising chickens and so far so good until a chick I bought from someone. She is supposed to be a polish hen but we got her from someone who had hundreds of chickens in not the best conditions. We purchased her and three other and seperated them from our established flock. One died the next day and two are doing great. Polly has what looks like sour crop. I am giving oil drops several times a day and massaging it but it is not going away. I also give probiotics, apple cider vinegar in water. She has medicated chick food. She still runs around eats and drinks and acts like she is ok. So could this just be how she has developed? Any thoughts or guidance strongly appreciated. Thank you