We sent her a letter clearly explaining the consequences, and she moved out.   

Use a skip tracing company to find their number or send them a short letter asking them if they want to sell.

. - I don't really mind mixing investment with personal if it is something that I take over after 15-20 years.

Everything I’ve found online is either “personal residence” or “rental property” so obviously this is a mixed bag and creates some confusion.

If there are funds remaining in escrow, you will also likely received a letter of direction to pay your legal fees from those funds.If something arises during diligence which cannot be resolved and the deal falls apart, you still may have incurred some cost from your attorney's efforts. 

I don’t like mixing business with friends, but she was in a tough situation so we are doing month to month as she finds a new place.

Thousands of letters.

@Kyle J.As far as I’ve been told all I would need is a Letter of Commitment, (looked over by a lawyer of course), vs an actual mortgage license Thanks again!

The foundation repairs are a good negotiating card for you and with an engineer letter stating what needs to be done exactly done and a quote from the engineers trusted contractor, what argument can the seller make? 

My current plan is to let her know my intentions in a conversation and let her know a formal written notice will be issued by end of the month.Another concern i have is how to deliver written notice, is it as simple as handing a letter to them, or do i need prrof of it somehow, i.e. have them sign something having received the notice.