Hello and welcome to BYC!
So sorry your bird has sour crop. Is the crop hard like a soft ball? (Impacted crop) or soft and squishy? (Sour crop) If soft...Make sure not to be feeding foods that feed yeast....bread, fruits, berries, etc... stick to protein foods only and chicken feed. A round of Acidified Copper Sulfate in her water for 7 to 10 days will help if this is a simple yeast infection.
If the the crop is hard like a ball, she may have a grass impaction. Plain Docusate Sodium 100mg (stool softener, no laxative) will help dissolve the impaction. Squeeze out 1 pill a day for several days, onto scrambled eggs, make sure she eats it all.
If your flock has not been wormed in the last year, worms can impact the intestines and slow down the waste exit. Some Liquid Goat Wormer will deworm them all. Coccidiosis can cause slowing of the intestinal tract as well.
You can also post a thread in our Emergency forums for more help here....
https://www.backyardchickens.com/forums/emergencies-diseases-injuries-and-cures.10/
I hope she is ok!