I'm uncertain about recording a deed with only partial ownership.

The lending market is quite competitive these days and you might be able to find a 30-year fixed if you have the personal income to support the loan.Without knowing the particular details on the unit it's hard to give a full opinion, but if it's in Boston proper, even an unusual unit should sell relatively quickly at the the right price.

I've never seen that disparity in over 500 houses, so that is most unusual @Kyle Myers.  

I know we are in an uncertain time right now and I am trying to work with her but her lack of response is making it impossible.

@Michael Giaquinto it seems highly unusual there wouldn't be any rental comps. 

Not terribly unusual.

I told him face-to-face in no uncertain terms to stay off my property and I was prepared to involve authorities if necessary.As @Marcia Maynard says you will need to be very diligent about monitoring the state of the property.

I am at 100% collected, which is actually highly unusual for this early in the month. 

Get them on your lease (with a security deposit that the seller procures for you and conveys to you at closing) as soon as possible, so you know what their lease says.With such a close-to-market rent in this uncertain time, I wouldn't raise rents until you for sure want them out.Have a walk through of their apartment and note any damages.

In our area it is not unusual for tenants to pay 40-50% of their income toward rent.