Chicken with lice issue now very sick - Page 2
Featured Stories on BackYard Chickens
It sounds like you are doing all you can do.
Peritonitis is basically eggs (usually yolk and white, sometimes shell) that has travel back up the oviduct or has "missed" and are dropped into the abdomen. The abdomen then can become infected and fill with fluid (egg, pus, bacteria, etc.) and cause a lot of problems. Some people try to drain the fluid and some do treat with antibiotics, these methods are generally used to give comfort and supportive (relief) care.
Stance, shortness of breath (fluid building up), weakness/lethargy.
Hopefully the antibiotics will give her a bit of relief.
Here is more information on Peritonitis and other causes of "swollen belly":
Edited by Wyorp Rock - 4/24/16 at 9:54pm