I thought feathers lost their blood supply after a certain point? Depluming mites are hard to reach while in the feather, but they have to move across the skin to find a new feather to inhabit.
If it's too cold to "brood" your Silkie outside, perhaps you could bring her and some heating outside each day, once her feathers are de-oiled and fluffed. Doesn't matter if it's wet, so long as the chicken and the heater stay dry. Fresh air is good.
Okay, I see. How much is it going to cost...
Shouldn't the chicken wire keep the other birds out...? Or do you have a bird-secure coop / small run with a larger unroofed area where the food and water are?
It looks more like a fungal infection, with the peeling and the chunks and the dry surface. Also you've treated with four different...
First, find some way of keeping the wild birds out of the food and water. You can keep on treating problems, and the wild birds can keep on bringing them in. I see you have an enclosed pen there -- can it be covered with netting? If it's too large for that, can you partition it and put a cover...