With sour crop we never feed them anything because it only fuels the sourness. Water only for 24 -48 hours with regular massaging to work it through. I don't attempt crop draining. When the poos have lost their stinky slimy quality and the crop is completely empty and cool she can go back onto a normal diet. Don't worry about feeding her. She should be able to go weeks without food.
We have had cases where the crop has gone sour because of an impaction. Treatment is the same. We have also had cases where the crop has gone sour because of a gizzard impaction due to grass, which is irreversible. But the crop is draining so that's not the problem.
You will need to watch for reoccurrence. If all the sourness isn't removed, or if the cause is cankers, different treatments apply.