Between state income tax, property tax, weather related expenses, lawn maintenance, etc. 

If they are discounting the value of the property from the start, that means you owe them an artificially inflated amount later.

If you are talking of the BP calculator I usually do it on a per building basis so I add up the rents just because the mortgage Is for the whole building and expenses like water, insurance, taxes lawn care, snow removal will also be for the full building makes it easier to compare apples to apples

Another option you have is maybe see if her son would be willing to do some upkeep on the property lawn care and what not for a slight discount on the rent to get the numbers closer, it saves you lawn maintenance costs.

I’ve got maybe $300 in patching to do to the lawn if they moved tomorrow.

I don't have tenants watering lawns at rental apartments.

On average I figure it takes me 14 hours/ month to manage it. 8 hours/month to visit the properties (2 per week) because I like to make sure lawn maintenance is being kept up with, plowing is done correctly, trash is picked up, and coin laundry is checked. 4 hours to deal with banking and bill payments and maybe 2 hours to deal with actual tenant issues.

I owned a lawn care business catering to upper middle class doctors, lawyers and such for nearly 30 years and I carry that "No mistakes on my watch" attitude into this business (while still being unflinchingly strict on the other side when I need to be).

Think of all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

Unless it's a single family home in which case tenants will also be handling lawn care.