I have looked at the photo closely and it really does look like her crop. They can hang down quite a bit when they are full!
A few things for you to do now:
1) Observe her carefully. Does she seem lethargic? Does she eat and drink well?
2) Palpate the crop and see how it feels. If you feed pellets or crumbles, these turn to moosh pretty quickly in the crop. Grains and mash will remain mostly whole. Does it feel like a water balloon, perhaps with some food inside, or very hard and tight, solid?
3) Check her breath, if you can. Does she smell sour or yeasty?
4) Check her crop when she goes to roost for the night. Then, the next morning, check again BEFORE she gets down and feeds. It should be much smaller or even empty if it is operating correctly.
Are you sure she is the one plucking her own feathers? I have one bully hen that loves to pull feathers off of the throat and chest of one of my other hens.
If your hen is doing this to herself, you might be right that she is experiencing a problem in this area. While I am still fairly new at chicken medicine, I can tell you that when parrots pluck this area, sometimes it is due to infection or yeast in the crop.