That looks like a normal cecal poop to me. :) Every eight to 10 poops, an oily-looking poop will appear. Totally normal.
Your vet can run a test on a fecal float to confirm the presence of cocci or any other parasite your chickens might have.
Since Corid is a really gentle medication, you could run it through your flock's water every now and again as a preventative. :)
Hope that helps!
Thanks MrsB! I have some Corid, so I will start with that. Hopefully it will clear her up. She is the only one with this issue, and I would like it to stay that way! I have noticed the run has a lot of these runny, dark looking spots all over it, and I really don't want the others getting it too.