Well, you have one with sour crop correct?
There usually is an underlying cause (worms, coccidiosis, reproductive problems, infection, etc.) but if the crop has gone "sour" then she probably has yeast/fungal infection along with whatever else is going on.
Fenbendazole is a dewormer (anthelmintic) while Nystatin is an antifungal medication.
IF you think that she has a worm infestation that is causing inflammation or slowing the digestive process -makes the crop not empty/turns sour, then you would want to treat for worms, but the sour crop (yeast/fungus) needs to be addressed as well.