Have you tried DE (diatomaceous earth)? I love it and it kills the lice and mites. I use it on my chickens and rabbits and it's all natural. You just need to keep it from lungs and eyes. When the chickens aren't around I sprinkle it where the chickens take dirt baths. If I think one or more has a problem I will sprinkle it on their back with a salt shaker I purchased for just that reason. It has worked wonders for me.
Yes, I use DE, I put it in their dust baths and I sprinkle it in the main coop floor every week too. But I don't ever really see the Silkie's dust bath, I couldn't find any on my other birds, I looked for an hour last night, just on the Broody Silkie Momma that is sitting on eggs right now. so hmmm.....
Hens go broody when you don’t want them to… and won’t go broody when you do. 
