That's really odd looking poo, is it black? I've honestly wondered if she has some kind of cancer that has filled her belly with fluid?
HOWEVER, When I watch the video of your hen she doesn't look like she's in any pain at all, she looks curious and very happy.
As long as she's eating, drinking, pooping and puttering around there's only so much worrying you can do.
Thanks for posting the video, she's beautiful. Does she boss the cat around? My chickens love cat food. It's like chiclen crack or something.