What could've happened to Fatty?

[aart]

I thought they started molting in September... maybe a bit earlier this year, thanks for the explanation

I've found over 10 years that they can molt anywhere from August to December.
Each bird is different, the males usually started first.

 

[LaFleche]

This year, my older hens even started in July!

 

[rosemarythyme]

I agree, likely a molt, especially if you keep seeing piles of feathers wherever she hangs out. I have one older hen down to a single tail feather, leaving little piles of feathers everywhere she's been the last few days. And judging by feather colors, two more birds are beginning to molting lightly.