If you are having trouble finding Permethrin this could be an alternative.Do you know where I could buy permethrin dust in England? When I search it up only Diatomaceous Earth comes up. She did angrily dust bath the first two days but her dust bath got wet in the rain and I didn’t have any dry dirt to fill it up with.
I haven't tried it but it is being recommended by some fairly reliable sources.
https://www.stdavids-poultryteam.co.uk/news/dergall/
https://shop.bhwt.org.uk/blogs/news/dergall-new-red-mite-treatment
https://www.chickenvet.co.uk/dergall-100ml