We have a niece like that.   She has systematically attached herself to every source of support and potential support, extracting without constraint and without conscience and always back at it despite expert treatment stints that she seems incapable of seeing through.  It is so very sad, and so far beyond anyone's ability to deal with.  There is a demon in that young woman we'll never know; she can't stop taking, and she drags down any loving soul who ventures near.  At this point, it is very difficult to imagine any outcome that is not destructive or tragic.