Losing their feathers is perfectly fine!
Molting is when chickens lose their feathers. This happens every year, and there is nothing wrong with your chicken. The feathers will eventually come back. Mine molt about every fall, and they look like something pulled all the feathers out of it. I could make another chicken with all the feathers that accumulated in their coop!
Two of my chickens look horrible right now.
This is what they look like before molting...
The feathers are lost from the head first, followed in order by those on the neck, breast, body, wings, and tail. It is okay if it is not in this order. One time, one of my chickens lost its tail feathers before anything else.
After a while, you'll see the new feather shafts poking out of the skin.
Behind my nosy Bantam is one of the Leghorns that are molting. If you look, there are white things poking out of the skin. Those are the new feather shafts.
I hope this information was useful!
(these pictures and chickens are all mine)