You can use seven dust bought in the garden section of any garden or retail store, like fleet farm, true value, menards may have it......
TSC should have it, don't buy the chicken dust, in my opinion its useless and I wasted 30 bucks on a 20 lb pail to no avail didn't get rid of them until I used the seven dust.......... vet recommended.
Yes mites can make your chickens ill or kill them, they are blood suckers and will slowly bite them to death........
Get her to eat something, even if you have to go out and dig her some worms.................. fresh water with Apple cider vinegar, 1 ts per quart to help clean her system and add some good flora for her belly, use only braggs organic with the mother,, poly visol, or baby vitamins, yogurt, plain greek is best.... if you have Kefir or know anyone who has some give her a ts in her food, scrambled eggs, are great........... the more food she eats the stronger she will get............ and treat immediately for the mites... if they are really bad give her a bath using dog flea and tick shampoo, then when dry dust with seven, have a helper if possible 2 ppl works best, have your partner hold her head under his/her arm while cradling her in the crook of the arm, but not upside down, start at the tail head and sprinkle lightly working it down to the skin with your fingers, do her whole back, under her wings, and her neck keep it away from her face and don't breath it you or her..
You will have to treat all your birds, and clean there quarters well throwing out the litter if possible and sprinkle it every where nest boxes, floor roosts....ect............ they are not easy to get rid of, re treat in 7 days. after this add some to there dust bath once a ,month with some DE sprinkled in, you can get that at alot of feed stores but get food grade not the gray crap mixed with benenite clay.
you can also feed them some DE to help with worms 1 tx a week mixed in with some scrambled eggs or something fairly wet so it sticks and isn't powdery, it's not good for them to breath it....you either, its microscopic fossils that have tvery shape edges and they kill worms by cutting the exoskeleton and they bleed to death, it will not hurt the chicken or animals because it so small. it can hurt the lungs though so always mix it with something wet or at least moistened. to cut the dust. I hope she makes it............ will pray for her.......Kim