Is she pooping?
I would go ahead and start treating the crop. Worming her as suggested may be a good idea too - often a crop issue is a symptom of an underlying condition (worms, reproductive disorder, etc.)
Could be she's a little fatty. Not all reproductive disorders have swelling or fluid, first indication may be that they are acting off/not feeling too well.
I would re-check that crop first thing, if it's empty, that would be good. If it isn't, then try to decide if it's sour, doughy, etc...
When is the last time she laid an egg? Any bloat/swelling or fluid in the abdomen?
I agree, getting a better look at that poop would be good. The yellow is concerning to me - either it's "eggy" or the urates are yellow.
I would check to make sure the crop is empty first thing in the morning...