Chicken abdomen like water balloon
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It sounds a bit like possible ascites or fluid in the abdomen. This can happen with heart failure or liver disease, but is also sometimes a problem with internal laying and egg yolk peritonitis. Yor chicken sounds like that. Pictures are always helpful. Fluid in the abdomen can cause shortness of breath and labored breathing. If there is fluid present, you can take an 18 gauge needle and puncture the skin to drain off fluid, which is usually yellow if from ascites. Here is a link about this:
photo by Casportpony of a hen with ascites or water belly
I'm so glad that you were able to have the vet see her and help. I really hope that she gets better. If she will eat, feed her chopped egg, tuna, liver, or ground meat for extra protein. Since she is severely wasted, you may want to try tube feeding her two or three a day. Vets have the feeding tubes and a catheter-tipped syringe. You can also use a piece of aquarium tubing fitted to a regular tip syringe, but the end that goes into the beak must be rounded off with a lighter so it's not sharp. KayTee baby bird feed is usually used for tube feeding, since chicken feed is too thick. Here is a good link about tube feeding: http://www.backyardchickens.com/t/805728/go-team-tube-feeding
She's sitting in a warm water bath right now. Got her to eat oatmeal with some of her food mixed in, some watermelon, and a couple raisins. I've been forcing her to drink more water. I felt up in her vent and can't feel anything, but vet said the blockage was high. I'm hoping that the antiinflammatory drugs and the antibiotics calm everything down enough that she passes whatever it is.. Likely egg fragments. I know her odds aren't great, but I would feel terrible if I put her down without trying something.