What is wrong with my chicken's feathers?

[OwO]

Hello, I have posted a few times about this hen before, she is around 9 years old and a Barnevelder. She has itchy crusty skin a lot of the time and has clumps of crust around the base of all her feathers. When trying to remove the crust, the feather often comes out as if it were barely even attached. They look like this:

You can see there's the normal feather "stem" thing, and then there is a secondary smaller one which is also sticking into her skin. I think the dried crust is probably pus from where it's growing into her skin. When I remove the crust from the feather after it has been removed, I can see the secondary part contains a small amount of feather material:

All of the feathers on her neck and head appear to be like this. While I am not purposely pulling them out, she seems to get really itchy on the back of her neck and tries to scratch it but can't reach completely. I itch it for her and the feathers will occasionally come out while doing so. Here is what her head looks like:

Would love to know what's going on with her and if there's anything I can do to help her. Thank you!

 

[Wyorp Rock]

Hard to know exactly what's causing it. I think she's had an chronic skin condition for a good while now right?

Does applying an anti-fungal/yeast cream seem to help at all or have you tried the dandruff shampoo as suggested in one of your other threads?

It may be that you'll never really know the answers as to what is causing all of her symptoms unless you lose her and have your vet lab/agricultural lab do some testing/necropsy.

https://www.backyardchickens.com/threads/favus-will-not-go-away.1557511/