Thanks for the pics. You're correct, tough to tell if it's a worm. It would be best to clean off the feces from her rear end and do the same for all your chickens. Feces stuck to feathers can and will attract flies and you dont want that to happen.
I use a garden hose to spray off their rear end and it works great. Of course if it's cold outside, dont use the garden hose, soak their rear end in a container of warm water or just use a wet wash rag to remove the feces. Dont forget to wear disposable gloves.
Sometimes green colored feces can be an indication of worms. She is your chicken and go by your instincts since you are concerned. I would go ahead and worm her, as well as your other birds. The wormer wont harm them, and will help them by eliminating worms. I worm my birds monthly.
I recommend Valbazen or Safeguard to worm your birds. I prefer Valbazen. It lasts longer with less dosing.