This is really wonderful. I was apparently limiting my perception of the obsession to the romantic friends 11th, romance 5th, or partnership 7th houses. Knowing that the Griffith/Johnson relationship started when Melanie was 14 puts a whole new perspective on the obsession, and then the 4th house as a site for the obsession makes real sense.
I can always expect someone here to bring some obvious perspective when something really really obvious escapes me. Thanks everyone, especially Jon.
Interestingly, her Klotho(the asteroid of beginnings) inconjuncts his Pluto. This brings a compulsive spice to the Pluto/Sun conjunction(SORRY DON), and the fact that its an inconjunct meaning that issues tend to come from behind, in a totally unexpected way, which is what obsession tends to do, is another point.
But having missed the connection by limiting myself to strictly romantic relationship houses, I wonder if I could find the charts of well know brother/brother/ or brother/sister, or sister/sister teams who were obsessed with each other in a taboo 3rd or 12th house way? Unfortunately astrodatabank hasn't been helpful so far.