#1 or #3 make financial scenes.

If you want to help her out financially, this is not the way to do it.Now to specifically answer your question.

As a general rule (as I have been told by financial advisors), you should not put money into the stock market unless you are planning on leaving f it there for 5 years.If your investment is 3 years off, I would consider investment in a note fund that has a 3 year maturity.

For me (and my personal struggles) I found military schooling to be very financially challenging when it really shouldnt be.

However, you may have a hard time finding a seller who will take second lien because they potentially end up with nothing (not even a property) if your financial situation goes belly up. 

If not, then I'd say it all comes down to your financial situation. 

There are tow reason to get into REI as I see it.1 - Financial. 

I would consult a local attorney about this to be sure you are complying with state laws.I am not a lawyer and do not offer legal advice.Just my personal opinion but,if the tenants property was damaged or destroyed through no fault of there own,it would be the landlord’s financial responsibility to make the tenant whole and their insurance should pay for the damages to the home and the tenants belongings.Again,check your local laws with an attorney.

Here are their financials for last 3 years, with specifics taken out to protect the innocent.71 lots, 45 TOH's. 

Working with This tenant and property manager seems to have a lot more financial risk than denying the applicant.