The funny thing is there are usually many cranes in the air downtown.

Running a vent for central air is not a problem, but you will likely need a return air as well.

Option 1: pay around 20K to install new HVAC/minisplit system.Option 2:  pay for heating and cooling as a service which is about $350 a month without installation fees for 10 year contract, they do all needed repairs and service a year included, write it off as a service. when I sell pass the cost/contract off to the next buyer. details at: https://www.knochelmann.com/advantage-program/heating-air-conditioningHas anyone had anyone used something like option 2 and what are your opinions?

She wants to sell the house to me for only what she owes on the house, so it could alleviate some pressure from her financially. 

I have been running the rental calc over and over again on different properties and I am not getting the return that every expert talks about.My next game plan is looking for SFR that may have an in-law suite or full basement to even Air BNB

If she doesn't provide the letter and is just trying to manipulate you with the threat, she can get her own air filter. 

Less pressure.

Growing up  I always wanted to be a fighter pilot for the air force. 

But with the relatively low CAP, Heloc would be a better choice for this property to avoid unnecessary pressure on the negative cash flow. 

Air Bnb?