Hi, welcome to BYC!
Sorry for your loss.

I'm on the CA/OR coast and you are right the smoke is taking it's toll on many.
Your first death actually sounds like Marek's was a possibility.
Beyond that... with all the prolapsing sounds like you got some bad genetics possibly.
Is it possible your most recent girl was egg bound? Any chance you can refrigerate her and send her for necropsy?
We have fought lice and mites this season. Some mites are microscopic. The permethrin spray is very effective, safe, and affordable. I would buy it and treat if you haven't previously treated seems impossible to avoid parasites all together when you live with such a bounty of wildlife.
Also, have you ever treated for worms? A fecal float is about $15 at the vet to make sure you treat for the right species if you even need to.
https://www.backyardchickens.com/threads/how-to-send-a-bird-for-a-necropsy-pictures.799747/
https://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf
Your hen very well could have been brought down by the perfect storm combination of things. Only real way to know is necropsy.