It's been vacant for at least 5 years, so they've spent at least $18,000 in fines alone, not including taxes and homeowners insurance and lawn maintenance.

Communication around the turn over was excellent and the move out report and repair estimate was in line with a move out with only minor paint touch up/lawn maintenance/rekey/etc type expenses. 

If so, you have essentially two options: grade the hill back gradually into the lawn and plant something on top of it (grass, groundcover, whatever) or put a new wall back in its place.

Toilets are some of the biggest water users.But go down the list, check if lawns are over water, is drip irrigation in place, water efficient toilets and shower heads etc.Check for leaksThis is very solvable - Best to you! 

Does it include lawn care snow removal or does the owner do it himself so the property cash flows better?  

Property maintenance such as mowing a lawn to avoid local fines can cost money every week or two.  

I will have it typed up so we can both get it signed and notarized so it'd officially I will clean up and mow the lawn.

A few years ago , she felt that I was harassing her by checking on the lawn once a month (driving by).

There are a tremendous amount of people convinced they can make easy money and get a steal that they shampoo the carpets, mow the lawn and make an easy $25,000.

Since you have held rent artificially low, it has trained them to believe that is normal, which is not the case.The hard part is that you waited so long.