Does it feel like only food in there? Do you see the other lump in your picture on her left front? What does that feel like?
If that is the crop, it's not in the right place, and I've no idea why it would be there other than deformity. Does the crop ever empty? Try to feel it first thing in the morning before she's had access to food or water, see if it's smaller then. If she's pooping normally, then the crop should be going down. If it is a deformity, and that's hard to know from a picture, then sometimes chicks that have one will have more, some not obvious. So more may be going on inside, it's just very hard to know. I would examine her and feel for any skeletal abnormalities that may not show up with just a visual check, compare with one of the others that is healthy. She could possibly have ingested something she can't pass, but droppings would usually look different. I'm a bit stumped.