Okay...I finally got a picture. My chicken seems to feel okay, and is the only one of four with a problem, but there is a "sploot" sound whenever she poops. The tray is black, so it's a little hard to see.
give her probiotics. Human kind works, or you can give her yogurt too. Regardless of egg production or not, beneficial gut flora helps with immune response.
Check her vent pelvic bone width. If she hasn't started laying, you could probably fit only two fingers in the space.
You'll be able to tell if she's nearing her first egg as the width get wider.