Be careful with ash and diatomaceous earth especially, they can cause respiratory issues in animals and humans.
Our chickens have lice too and we plan on bathing all 32 of them in a mixture of castile soap, salt and vinegar. It's supposed to suffocate and kill all live lice and loosen the nits. Seems to work very well from everything I've heard, so we're going to give it a go

I believe you're supposed to repeat in a week, to kill any lice that may have hatched.
Here is the recipe:
Chicken Lice/Mite Recipe
5 gallons warm water (comfortable for your birds to bathe in)
2 cups table salt
2 cups white distilled vinegar
2 cups liquid castile soap
First, in a large bucket capable of holding 5 gallons of water (plus a chicken), mix and dissolve the ingredients listed above into the warm water. [Note: it may be easier to dissolve the salt in a gallon of hot water and then mix that to the bath mixture]. Make sure that the ingredients are well dissolved and mixed up. Also, be sure that the water temperature is not too hot for your birds.
Next, one-by-one place your chickens into this treatment bath. Be sure that the bird’s head stays above water. Each chicken needs to soak with their body fully submerged for five minutes. You often will see dead mites and lice float to the surface of the bath.
Rinse the treated hen in a second bucket of warm plain water for a couple minutes. Be sure to towel dry all of your washed chickens — you don’t want them getting ill. Chickens have a very difficult time regulating their body temperature when wet, so it may be wise to use a hairdryer and give them blow drying.
You can use the same treatment bath for several hens (as long as the water stays warm enough) for them.