Two things struck me: Jackie never lets herself get in the way of a good story. Others might have used experts' psychobabble to explain OCD (though that could be a sidebar), or bogged the piece down with overwrought emotion and wordplay. She let vivid descriptions and quotes carry it.
And her long, professional relationship with the Celtics opened the doors. Players clearly trust her. I can't imagine any reporter getting close enough to, for instance, a Knicks player who might be willing to share such a personal story. The organization would never allow it, and that's everyone's loss.