Water Belly?

[Brianna Williams]

This hen came to me a few years ago, already a couple of years old. At the time I noticed that her behind was kind of red and not feathered like the rest of the her flock mates that came with her. Her previous owner is an experienced farmer and didn't seem concerned so I let it ride. These days it's more pink than red but still quite large. Now I'm wondering if she may have water belly. She is one of my most active hens, total character, eats and drinks normal, walks normal, and doesn't display any pain behavior. Which is why it's been easy enough to leave it be. But it's certainly not going away with time. I've watched some videos and am prepared to drain her but I wonder if anyone else can verify my suspicions that it is water belly. I'd like to be as sure as possible before I poke her with a needle. I know she has a poopy butt in this picture so try to ignore that. I do my best to keep them clean but it is still winter here in Idaho so I'm a bit limited for baths. Oh and it's not mites or lice. We've been there done that (yuck) but she has been this way before we ever had the bugs and remains that way well after a thorough and successful flock treatment with elector psp.
I welcome any insight!

 

[nuthatched]

Looks more like she's being picked.