@unbaked pegga I'm very sorry to hear about your hen
Can you clarify something? You mentioned that you treated your coop and nesting boxes with Permethrin spray(?) did you also treat/spray your chickens too?
I agree with
@Eggcessive determine what course of treatment you want to administer to your chickens and stick with that. You can use the Permethrin to treat them
or you can use the Ivermectin, I would not use both at the same time.
If using Permethrin, you will need to re-treat your flock in 10-14days after your first treatment. Spray under the wings, around the vent, back of the neck, etc.
If using Ivermectin Pour On you would re-treat in 14days after your first treatment. Ivermectin Pour On should be administered to the back of a chicken's neck as follows:
1 drop for chicks or tiny chickens, 3 drops for bantams, 4 drops for lightweight birds, 5 drops for large birds and 6 drops for heavy weight birds.
Ivermectin is absorbed into the bloodstream, so an egg withdrawal (throw away period) should be followed. There is no really good information on withdrawal times, so throw away eggs for at least 14days after last treatment (you may want to research and find a timeline you are comfortable with).
I have never heard of diluting Ivermectin and using it as a spray. I'm not a vet, so can't say one way or another about that, but from everything I know and have read, it would be applied directly (undiluted) to the skin.
I hope all goes well for you. Keep us posted.