We are brand new to chickens. We have seven babies in a big cardboard brooder 3' x 5' in the basement with warming lights. They came in the mail 26 days ago and they were all growing the same for the first two weeks but lately one little Speckled Sussex is not growing as well as her sisters. She seemed happy and drank and ate with the other chicks and pooped the same but she is now half their height. Another friend said she was a bantam but today an experienced chicken guy looked her over and said she has a crop problem and he said she will probably die! His wife helped me take her photo and felt her crop which is soft and squishy feeling. We put her in an isolation tub right inside the big brooder so she can see the girls but they can't hurt her. No one was picking on her until tonight when I saw one of the Barred Rock girls peck her neck. In the isolation tub she is eating her lettuce and baby chick food. She was not one of the chicks that had pasty butt. What can we do? Please respond if you can.