Mites are everywhere and wild birds spread them around, so don't beat yourself up because she got some. You are doing a great job helping her get rid of them now. I think hang on the with chemicals for a bit, you've given her quite a dose already, and feed her a little fresh garlic now and then. I heard that helps repel the bugs. Also diluted garlic oil applied directly to the skin.
Yep, totally agree, they are inevitable, you just have to keep an eye out and treat as needed. We have a free-ranging flock that gets closed up in a coop at night with only perches, nowhere to sit in bedding, and we still have occasional problems with mites and lice. All our birds have been looking and acting great lately, yesterday I saw one hen sort of scrunched down and occasionally closing her eyes, picked her up and sure enough, lice and eggs. I would have never known if she hadn't shown me they were pulling her down, everyone has been looking so healthy. In the past, we've usually caught it by watching the feathers in the vent area, and if they're fluffy and pretty they're usually fine, when they get dumpy and yucky looking, feathers sort of matted a bit, that's when we know we have something going on. This is the first time we've caught something when everyone looks so good, just goes to show that these things are always out there and it just depends on the health of your flock as to who gets pulled down and how quickly. I suppose you could also do a periodic check and treat as you find them, that would get at the bugs before they are too much of a burden. I know people can lose chickens to these nasty little bugs fairly easily, so best to treat before they are too down and depressed of course.
If you got a good bit of sevin dust on her, that should be sufficient. It will kill the non-egg bugs fairly quickly, but it will take more time for your hen to recover her strength and health and for her to look good again, additional treatments with chemicals won't help turn her around at this point- just good ol' supportive care. Just remember, it's critical to treat with Sevin dust again in 2 weeks to kill the bugs that will be hatching out of the eggs. I think I would leave it at that and not do any more ivermectin. I personally have not seen much of a result from DE and as much as I hate to use chemicals, this is one time that I don't hesitate to grab the permethrin/sevin dust... Hope your hen recovers quickly and can finish hatching out those chicks!!
