What is Wrong with my Chicken?!

[KadeSilkies21]

So my ISA Brown hen (unsure of her age) has a very nasty butt. I checked on my flock and noticed that all of the feathers surrounding her vent were soaked in black/brown runny poop! I immediately got the hose and gently tried to wash it off. Her vent was red and a bit swollen. Does anybody know what this is and how to fix it?

 

[PatrickRoo]

Can you post some pictures of their vents? If I'm not mistaken, this sounds like Vent Gleet.

 

[KadeSilkies21]

I'll post some pics soon.