I'm actually interested in repeating this approach with future rentals, as I love to be environmentally friendly and imagine solar panels becoming more trendy in the future. 

Gold in it with writing down your 20 to do/want to dos, picking your top 5, and consciously saying that the other 15 are "never dos".

Put her a** on the street and get your house in order.No idea why you have asked for advice when you have made a conscious charity based decision and been acting as her social worker for 4 months.

And also unlikely that it spilled enough oil into the soil to really be an environmental problem for that small property.  

You do need some legal advise and you might go to someone who is well versed in environmental issues or look for someone who has dealt with dams/water issues, that is the closest I would imagine getting to owning a lake bed.

This is important because if they process dry cleaning on premise there could be environmental issues.

Environmentally, there's a lot of resource waste that, for those who are environmentally conscious, is not ideal.

I plan on continuing, growing my REI as a profitable yet legal, honest,helpful and ethically conscious business.I have nothing to hide and I believe that having the support of an experienced and success promoting broker would only benefit my endeavor. 

I have purchased houses with asbestos siding (which is incredibly durable) and as long as you don’t break the tiles it doesn’t create an environmental hazard.

Because you are asking this question it sounds like you are more conscious and thus probably are a better landlord than most.