Poor Feather Health - Please Help with Finding the Cause

[Jazzin]

I have a hen that has patches of feathers with snapped shafts and loss of barbs on her neck and breast; images are attached below.
She lives with one silkie hen that is quick to put her in her place by grabbing her by a feather in the region with broken feathers, but from what I've observed isn't a bully. In fact, the two are virtually inseparable most of the time. I treated the two for lice recently, but the hen with all of the feather breakage had hardly any nits on her, while the silkie had a more serious problem but only some feather damage on her belly and none on her neck/breast, making me unsure that this is the cause, neither. I have considered depluming mites and I am very curious about them, but I haven't been able to find much information on diagnosing them and it seems to me that most birds with depluming mites rip their feathers out entirely and don't leave the shafts, leaving me unsure once more. Perhaps there is a combination of problems causing this? It seems to be very slowly getting worse over time. Any opinions are welcome, and thank you for the help.

 

[Wyorp Rock]

She lives with one silkie hen that is quick to put her in her place by grabbing her by a feather in the region with broken feathers, but from what I've observed isn't a bully.

I treated the two for lice recently, but the hen with all of the feather breakage had hardly any nits on her, while the silkie had a more serious problem but only some feather damage on her belly and none on her neck/breast, making me unsure that this is the cause, neither.

seems to be very slowly getting worse over time.

Getting slowly worse over time...but the Silkie pulls her feathers, so it would be logical that the breakage and loss would get worse as time goes by.

What did you use to treat the Lice? A permethrin based poultry dust can work well. Put the dust in a sock, then use it like a powder puff to dust all over the bird, working the dust all the way through the feathers to the skin. Repeat in 5-7day intervals for a few weeks.

If she still has nits in the feathers, you can either pull those out or put some coconut oil on them to help loosen the egg sacs to reduce the numbers. Put the nits in a sealed container and dispose of them.

Broken and damaged feathers will not be replaced until molt.