Legally she has nothing binding to back up her cost for the house repairs, I don't believe this would end well on her end.

I initially put in a offer for $630k, but was outbid by another all cash buyer and placed as back-up offer.

I let my brother (who is now 27) manager it and it went downhill from there so I came back up to take care of the properties.

If people say they can't make it at that time, I take down their info and contact them again if the showing doesn't end up getting it rented.Another option is installing a combo lockbox, then having the interested party call or text when they arrive and then call when they've locked it back up (obviously get as much of their information as possible to mitigate the risk).  

If that buyer isn't interested whats the backup plan?

If the heat is radiators from a boiler, you have to separate the supply piping and return piping for each unit, then you need the extra boilers as well; you might be able to re-gun the oil boiler with something like a Midco Economite to save some money on a boiler, assuming existing boiler is in good condition and not too oversized for the biggest rental unit.One thing to point out is that you will now have multiple burners.

But, it requires that we continually buy properties so that we can continually renovate and do cost segs otherwise, at the end of 5 years, the deprecation write off drops and our AGI goes back up. 

HOWEVER, from what I understand, there is something called a backup Buyer?

We had lots of cash on hand but warned investors in June of the potential for a cash call in September if leasing didn't pick back up.

As for investing it into a ETF or mutual fund, it may go up, or it may go down so if you're planning on this loan being the key to start your real estate investing have a backup plan in case the worst happens.