Final update: She died.
I cut her open to see what was blocking her up. I found no sign of what I thought I'd felt inside her crop. There was straw and shavings in her crop, some oyster shells, spinach, raisins, and scratch grains. Nothing that I found was blocking her up crop-side.
Her gizzard was huge, and stuffed with what looked like really fine-grain, almost powder-fine sand. There were oyster shells and some coarser grit too, but a lot of the fine stuff. I haven't looked into what a healthy gizzard should look like yet, but I wanted to get this out while it's still fresh in my mind. I did not take any pictures.
I also checked her vent-side. I found no traces of egg shell, but there was what looked like cooked egg yolk all throughout. I guess I also need to look more into what it means to be egg bound.
This totally sucks. She was the first hen in this flock to get a name, and I grow very attached to my pets.
Rest in peace, Hot Mama Jamz.