I have heard that coconut oil will drown the little buggers if you want a more natural approach, however I have not used this approach. I have used something called CatronIV as a preventive on my wounded rooster, and believe me he had a huge wound. I've used it now once a week for the last 9 weeks, and there seems to be no ill affect on my rooster other than the fact he doesn't like getting a little wet. It was recommended by my vet, and I picked it up at his office. I did notice later that it was at our farm store as well for the same price my vet charged. It's $12.00. It is a fly spray, and it will say it's for cattle goats and horses. But my vet recomended it, and if you look closely on the back of the bottle it says it for poultry lice as well. I assume it would work on mites also. It has 0.50% permethrin in it and the rest is other ingredients of which I have no idea.
Very interesting and informative thread. Wish you the best of luck in your hen's recovery.