Maybe change the word "vulture" to "Investment".
So far I have not read of any situation where an investment fund has been anything other than extremely reasonable and far more reasonable than the banks.
Of course if you read downtrodden newspapers with their scaremongering and catastrophising commentary based on no actual proof other than some blabbering by left wing politicians and people like david hall (5m house in dalkey is a bog standard house), you'd be worried.
There's a very strong possibility of buying out the mortgage for less than the value of the outstanding mortgage as "investment funds" are practical and are simply looking for a return on their investment.
You could collectively loan her the money to buy out the mortgage and have her repay you at a nominal interest rate over a long period