At the end of "Story of O" two distinct different endings are mentioned: One is, O receives permission to end her life, the other, that she returns to Roissy.
To me, it seems as though the author has had trouble with how to end the Story of O.
One should not advocate for suicide, especially not at the end of a fiction of this kind. On the other hand, how then, should it end ?
I like the 2. part for the attempt it makes at making a convincing end, only it fails to do that. I prefer to read Story of O as a story that has no end.
So read part two as an attempt, which the author chose, wisely, not to include in the outstanding work: Story of O. Nothing more.
One final point, which it took me 10 years to realise.
The title: Story of O in french is: Histoire D'O. Fine, but now try pronounce this:
Histoire D'Eau. The history of water. Even the title is a clue. :-) Water cannot, and has no, end.