I am not a lender - but in theory you can borrow to add a garage, or unit, etc.

Saves me $5k in borrowing costs, bs appraisal and bs lenders insurance every time. 

Some of us were worrying about Dad's borrowed down payment. 

Banks are out of the question if I am reading your post right, as they will insist the first 20-25% of any investment deal you do be your money- and they will likely frown if it is borrowed.  

Then you turn right back around and use your PML's money again on another deal, keeping them happy by paying them interest on the money you borrowed and keeping you happy so you didn't have to use your own capital

If you don't have your own capital, you also need to borrow transactional funding adding more costs to the transaction.

Say she does a 203k or conventional renovation loan she could have you joint on title as non borrowing or on the loan to help. 

(investor)A:VA loans want to net 88% of appraised value,Conventional will accept as low as 80% and reverse mortgage will accept 95% if the property is vacant if its occupied they will rarely accept anything under 5k of appraised value.Q:The owner is not the borrower can we do a short sale.

Private lenders have been opening up an 80% cash out option for well qualified borrowers.

If the borrower doesn't qualify based on those criteria I've found credit unions to offer nearly same interest rates, but with less requirements.