2 year old Barred Rock with runny poo is acting little lethargic Help!

Hello i have an approximately 2 year old plymouth barred rock hen who had a runny poop underneath her when i locked up the hens last night, this morning when i went outside to get eggs
i noriced that she had some light green poo stuck to her feathers. She had been sleeping on top of a nest box and when i looked there, there was a decent amount of green and clear runny poo.
Also today she is a little more lethargic than the other hens, we have been having some weird weather and they ate some watermelon the other day, but i dont think that that is causing it. I also was away for a couple weeks and the waterers appear to be slightly dirty and the feeder seems to have gotten rained on and some of the feed is wet.

any advice you can give would be greatly appreciated.

 

thanks. I also want to give an update. I just got done cleaning the waterers and the feeder and replacing the feed and water with clean replacements
im not sure if i should isolate her or not because i dont necessarily have a readily available space to put her. Do you really think that i should isolate her or not?

edit: Just recently i brought her a small handfull of sunflower seeds and found her in a nest box when she moved to get the seeds i noticed that there was and
egg yolk in the box. My new theory is that an egg formed without a shell and the watery poo was the egg white and nopw she "layed " the yolk also she is now acting
a little better and is a little less lethargic.