Liquidy/watery poop. WHAT IS GOING ON (picture)

[theabee]

UUGGGGGH! I can't figure out what is causing this!
One of my chickens has been consistently leaving very liquidy poops around.

It's been happening for at least 6 months- all winter long.
I gave all the chickens some "Rooster Booster multi wormer," which made no difference whatsoever.
The chicken who I think is leaving the majority of the watery poops also has a butt that has been pecked to the skin almost her whole adult life.
The chickens get fermented feed and pellets, a little bit of scratch sometimes, and free range a couple hours a day.
The flock is four hens, no roosters. It's my first flock.

I've researched this issue several times, and the only thing I found was that watery poops sometimes result from heat. But she's had this problem all winter long- it's definitely not heat!
One other thing- a while back, she had some kind of impacted crop, which seemed to resolve itself with an Epsom salt bath and a night in the house. She now has a bit of a pendulous crop though, that swings when she walks. I'm thinking maybe her whole digestive system is out of whack. What can I do to help her?

Thanks!