Green watery poop = bile, typically from not eating. It means she's not just sick, she's really sick. This could be a symptom of a reproductive disorder, but if so, then it's far advanced. I don't believe you're dealing with an eggbound pullet.
How does her crop feel? Hard? Squishy? Empty? (check the crop in the evening at bedtime and again first thing in the morning BEFORE she's had access to food or water. A healthy bird's crop will feel totally different at these two times of the day. How is her breath; does it have a sour, fermented smell? Does she have a dirty bum?
Other experts will likely chime in soon, and these are some of the questions they'll ask about and also what feed is being offered, including treats. It's likely that they'll suggest you put her in a dog crate in the coop so that she can be isolated, yet still within sight and sound of the rest of the flock. Isolating her with food and water will allow you to see if she's eating or drinking, and if there's any change in her poop or if she lays an egg, etc.
I'll keep you and your feathered family in my prayers.