I dusted everyone and the coop with sevin/DE mix, and it seems to be helping a ton. She has been looking good since yesterday morning (did it the afternoon before) and I can only imagine how relieved she must feel, and all the other girls, too.
So, when do I have to retreat everyone? And the coop is still covered in the dust, do I still need to retreat it even if the stuff is still all over (we're in a drought now and it hasn't rained in ages, doubt it will, either).
Thanks for your help everyone! I'm so glad to have your suggestions.