Kowalski, our Australorp, has an eating problem. She will eat large leafy matter (alfalfa hay) until her crop is totally full, which causes the same type of thing you're describing.
We looked all over this site and found that many people have done crop surgery, with some success. I don't feel comfortable with it, and most people don't do it under sedation, but they say the hen doesn't seem to feel much. There are also some good links to other sites that show detailed instructions as to how to do it. It seems to be something that people did when they knew that was the last resort, but the stuff they pulled out would never have passed otherwise (check the pics on BYC under "crop" "surgery").
There are also people who way that they forced their hens to vomit by tipping them upside-down, and that got something out, but some other people also said this caused their hen to aspirate the vomit and drown, so I didn't feel comfortable with that, either.
The third bunch seemed to feel that isolation, no solid food, and a combination of vinegar, yogurt, and molasses (you will need to research to find out the combination and the order) flushed out the bird and caused the acidity of the crop and stomach to change enough for the matter to start to digest and pass. I don't know if that was successful for them, but Kowalski's crop had stuff in it that could rot for a week and still not dissolve, so I don't think it would have worked for her.
She's a pet, so we took her to the Avian Hospital vet in Mission Valley. Pretty pricy (the whole stay and the treatment was at least $500). He got a some of the hay out of her through her throat with long tweezers, then put her in isolation with electrolyte water only (no food at all) for the next four or five days. The crop went down, but I think it was because he took the hay out first. He said that sometimes the impaction passes, sometimes not, but that the crop is only the first part and there can be other stops in the intestine, so you have to be careful. He's a bit grumpy, but he's the only guy that seemed to know his stuff, and he has chickens at home.
If your hen is like Kowalski, we had four days before she started ballooning to the point where we felt it was necessary to go to the vet. She started honking like a goose and making a funny motion with her head that indicated to us she felt the push up from her crop. She's still with us, and seems to be doing great in the overeating department so far, but we definitely took up all the hay in the coop. We also put the food in a container that has a narrower opening, so she has to work at it a little more, which slows her down.
Hope it helps a little. Good luck with your chickie.
E
