One of my 17-week-old Plymoth Barred Rock chickens seems to have a crop issue. Her crop is empty in the morning. When I check it mid-day and and in the evening it is squishy and has that deflated balloon feel instead of the firm round, golf-ball like feel of my other four chickens. This has been the case for about a week. I have tried giving her olive oil in case she has a blockage. I have also given her (and therefore, all the chickens) some yogurt and cooked rice. She seems to eat with the same interest as the other birds. She doesn't seem to be lethargic or have bad breath. She may have foamier/greener droppings than nomal.
Question: should I be concerned about her crop issue?