I'm really sorry to read about Cupcake.
This product and Permethrin II have the same amount of permethrin (10%) in them so your dosage was correct; however, Permethrin II is nearly half the cost. I wouldn't switch now as I know you have limited resources, but the next time you get a mite product, just get the permethrin/garden dust. The vast majority of folks here use that on their coop and dust their chickens. Then do that again in 10 days, and mites are gone.
Why this didn't help Cupcake's mites is a mystery. You may need to clean out the entire coop, get the chickens out it, and spray it well, then let it dry before putting new bedding back in there, and treat the chickens before you let them back in there. Be sure to be getting under their wings and vent too. The whole chicken needs to be treated. You've most likely got a source in your coop/run where those mites are living and breeding.