Internal laying and egg yolk peritonitis are common problems in good laying breeds. Ascites or fluid in the abdomen from heart or liver failure is also common. Oviduct cancer is another common reproductive problem in chickens. Here is some reading about those things...
I agree with Mrs. Bachbach to treat the chick for possible coccidiosis with Corid (amprollium) which is found in the cattle medicines of feed stores. In what area of the US are you located? Your hen is wheezing and gasping pretty bad. She may have a respiratory disease, or she could just be in...