Some investors with rental will put in a plastic vapor barrier underneath the carpet between the padding to keep from seeping into the floors.

But think of filing as your "insurance" to get rent and it will also start to set a new tone with her when she realizes you mean business and you can't be sucked into her BS communications.

The foundations didn't have any dampproofing to stop any moisture vapors from entering. 

I don’t want to be mean but people go downhill pretty quick with that disease so I wouldn’t count on her being there for that long.

She came home one evening to find the screen ripped from the window and a man sleeping in her bed.

We had one hell of an herb garden going in one on the side of our old house.

New vapor barrier in crawl space.

From environmental standpoint, u may want to collect groundwater samples along boundary of the property with the gas statiob to see if it has impacted groundwater as well as soil gas samples to see if there is potential for vapor intrusion.if groundwater not used, then principal environmental risk would be vapor intrusion which can be effectively managed with radon system and vapor barrier.Note that if the gas station is downgradient from your property (gwvflows towards gas station), vapor intrusion can still be a problem since vapors can migrate thru sewers, utilities and any conduits.

@Grant Schroeder You could also ask him to use a vaporizer if he insists on doing it, it is much more discreet and leaves little if any odor.

But filing now is your insurance that you get your property back in the most timely manner.In addition to filing, you can give a 24hr notice of inspection so that you can go over there and ensure that your tenant is ok vs just ignoring you.But if she has already given excuses of having bank issues, signs don't look good for her being a responsible adult.