It really sounds like either a blocked crop or sour crop. The sour crop is basically fermented grains and grass. Doing a crop massage may help out but you may need to treat with copper sulfate in the water. I bet Teach can tell you about doing that since he has pigeons. Here is another thing to try which will empty the crop.
You can start by putting an eyedropper full of vegetable oil into the crop and then massaging the crop.
This will soften the impaction.
Put the dropper all the way back in the bird's mouth and slowly push out the oil. Any vegetable oil is good: olive oil, corn oil, or canola oil.
Mix
1/2-cup baking soda
1 pint of warm water
Fill the syringe and insert it as far as you can into the mouth of the chicken.
If you can get hold of some soft plastic tube to put on the end of the syringe to insert that into the crop it would be a lot better for your bird and for you when you put the liquid into her.. .I use the plastic (15 cm long) they use on coat hangers on the hook part from a craft shop
Have someone hold the bird upright in front of you.
Slowly and very gently fill the crop, do not over fill and get liquid into that hole at the base of the tongue.
Gently press up under the chickens breast and slide your hand up to the crop. This makes the bird open its mouth and the impacted mess will come out the bird's mouth. Push the contents up and out of the crop and out of the mouth.
You can face the bird toward the ground to help empty the crop.
Repeat this gentle stroking pressure until nothing comes up.
If there the crop is not empty, flush it again until it is empty.
Once the crop is empty, give another dropper of oil.
Coop the bird away from other birds so it can rest.
Provide about a cup of water with 1 teaspoon Terramycin dissolved in it.
Give no feed.
Second Day
If the bird is droopy on the next day, put molasses in the birds water for about four hours (1/4 cup per gallon of water). (half a teaspoon for a litre of water)
Remove the molasses water after four hours and give the bird fresh Terramycin water.
The molasses water will flush soured food from the birds digestive system.