Put on weight? Could be fluid/infection-filled abdomen. May have ascites or may have egg peritonitis. All that crap in the belly puts pressure on lungs and heart, hence the breathing issue.
You can't do anything if that is what it is other than try a round of penicillin injections to see if it stops the infection, but it's genetic/hormonal and there is no prevention and no cure. That said, I don't know if that is what she has. Is her weight in the abdomen? Check the meat around her keel bone (breast bone). You may find she is actually thin.