It may be best to handle her for things like treatments in the evening when she has gone to roost. Chickens are generally quieter then and you can do more with them. Mites can live for 6 months in the environment so you will need to get it really well under control before you get your new coop or they will invade that too. I have heard of using creosote to paint the wooden structures - this kills the mites in the wood and also blocks up the nooks and crannies where they live during the day (not sure if you are aware, the mites only feed on the chickens at night, they live in the environment during the day). Another method, which I have found really useful in controlling external parasites, is to get a sack of builder's lime and sprinkle it liberally over all the areas where the chickens go, then hose it down into the ground. In the dry areas like the coop, just sprinkle it around and get it into all the nooks and crannies. It is really dusty stuff. My chooks didn't seem to mind it too much at all. As for the chooks themselves, those poultry powders I have always found to be pretty useless. The poultry vets will tell you to use malathion, I think you have to either spray it on poultry or use it as a dip for poultry. I have found that Frontline Plus has been excellent in deterring all sorts of ectoparasites in my birds. It is off-label when used in poultry (it's not registered for them) but I swear by it. Just a few drops on their comb and skin of their head every 4 weeks. I had a really bad problem with stickfast fleas until I used Frontline combined with the builder's lime.