What do her eyes look like? Are they swollen, cloudy, is there any discharge? If they are bright, moist, and clear looking, she's probably not blind, but it could be a neurological issue or some other illness.. You are being correct in making sure the chick eats. I would go back to where you got the chick from and see if there are others that have been sick, and see if you can get any information that way about what might be wrong. Chickens go through a lot of stress during the move from breeder or hatchery to store, and then to a new home, especially if you get them from a retailer they can be overhandled, trampled, chilled, overheated, squashed, you name it. Stressed in a number of ways. If it were my chick,, at this point, I would not stress it further by separating it from it's friends, but you do need to keep a close eye on it, make sure it eats, and be in touch with where you bought it. .