Welcome to BYC, Steve!
Sorry to hear about your hen. If you postIn this forum, an educator will be able to help. The Learning centre might have some articles on treating impacted/sour crop.
Welcome to BYC, Steve. If you've caught it early, chances are good that it can be successfully treated at home. I will tag a knowledgeable member. @Eggcessive always gives great advice.
I've had good luck using acidified copper sulfate (ACS). The stock solution is made up using 1/4 lb of CuSO4 (copper sulfate) and 1/4 c of white vinegar in 1/2 gallon of water.
The treatment dilution is 1oz of the stock solution into one gallon of clean water. Keep the treatment solution of ACS in the refrigerator.
First isolate the hen in a wire dog crate inside the coop with no food and just the clean, plain water to drink for the first day. Check on her often and give her gentle crop massages. If the crop is significantly reduced in size and gassiness after 24 hours with no food, make up a mash with her normal feed using the ACS treatment solution and switch out her water source to the treatment solution. Hopefully after 2 days the crop will be greatly improved. Keep her on the ACS water/mash for a full 7 days before you release her back into the flock.