I had a hen that exhibited the same symptoms. I ended up taking her in for a couple days, that is up to you (minor issues reintegrating). I put her in a dimly lit room and I gave her Pedialite which really helped her to perk up the next day. I gave her a little yogurt mixed with olive oil too. I think it might have been a stomach issue with mine. A little TLC and she was right as rain. I had another who was exhibiting the same symptoms but no where near as bad. Left her alone, just monitored, and she was fine.
As for a sour or impacted crop...the first sign is they will have pukey smelling breath and you won't miss it if they do. Just pick her up and take a whiff near her head, if she has it you'll know. Post if she has bad breath.
P.S. Does she have any discharge from her nostrils or eyes?