When I have a bird acting 'off',
and before I even think about any 'treatments' let alone administer them,
I isolate bird in a wire cage within the coop for a day or two....so I can closely monitor their intake of food and water, crop function(checking at night and in morning before providing more feed), and their poops. Feel their abdomen, from below vent to between legs, for squishy or hard swelling. Check for external parasites or any other abnormalities.
Best to put crate right in coop or run so bird is still 'with' the flock.
I like to use a fold-able wire dog crate (24"L x 18"W x 21"H) with smaller mesh(1x2) on bottom of crate under tray.
Then you can put tray underneath crate to better observe droppings without it being stepped in. If smaller mesh is carefully installed, tray can still be used inside crate.
Hmmm, my hens have lights on a timer. The lights turn on before I get out there in the morning. What would sour crop feel like? Can it kill a bird? Can I feel for it even if she may have eaten already?
Sour crop usually feels like a water balloon, full and squishy. Normal chicken crops usually only have golf ball size firm contents unless you've given them something such as grated carrot as a treat where they've engaged in a competition to see how much more they can eat than their mates.
I suspect sour crop too, and azygous can talk to you about the treatment ( real expert in crop problems), but i wanted to suggest you to check just for sure that she isnt rattling, or wheezing, or if she has mucus from her nostrils.