Here's the blister, the skin looked like it was thinning and it might burst. Her vent is to the left, the blister is under the vent, this picture is sideways. It is about an inch in diameter and sticks out about an inch as well. Feathers were trimmed earlier, she had been

She is alive at this point being held upside down, the thing sunk back in when she was being held like this.
Here's what it looks like when she's held horizontally
Here she is, dry plucked in a big tray. I took precautions with latex gloves and saftety glasses, I did not want to risk infection or disease because I knew the hen wasn't healthy but not sure why.
You can see the abnormal abdominal bulge.