The way I read that, the seller could at any time in perpetuity come back and devalue the property by removing that structure.It sounds like you need an attorney to advise you on the best course of action, but at the very least, a claim of "adverse possession" is worth looking at.

She can buy the note on the house but she won't be listing the house for sale without taking possession of the property through foreclosure or some other means (deed in lieu, etc).

The typical use of land contracts is to protect the interest of the seller (make it easy and cheap to regain possession of the property in the event of non-payment) with a less than stellar buyer.

For the tax liens, that is more of a long term commitment as the state you choose to invest in will very possibly have different laws and time frames as to when you buy the lien and when the lien is either satisfied or you are able to take possession, which is not an easy process. 

I will have to assume all responsibility and liability for any occupancy, and all responsibility, liability and cost of taking possession.

An investor should only focus on asset classes that possess compounding returns realized through compounding interest.

We had the long discussion on BP on adverse possession over it.

When purchasing a non-performing senior/primary note, does an investor have 100% control of the exit strategy no matter the amount of equity possessed by the borrower?

They countered at $139,000 and to close on 8/3/18, plus they wanted 3 days' possession so they could move out over that weekend. 

Here is a typical timeline for a rehab project and some time ranges of what you could expect:Step #1 Purchase Closing/Take Possession (Day 1)Stage #2 Planning, Permits, Bidding (1 week to 1 month+)If possible, you will try to start the planning before the closing to gain a head start.