She is:
The High Priestess (of the Tarot)
Explanation
I beheld a woman with a scroll in her hand
In her card in the Tarot she is holding a scroll.
And the crescent moon beneath her feet,
In her card in the Tarot she has a crescent moon at her feet.
And she sat between two pillars Whose names are B. and J.
I cracked it because I thought of Boaz and Jachin immediately.
And she said, "There are others Who are like me, but I trump them all."
According to wiki: The High Priestess is the second trump or Major Arcana card in most traditional Tarot decks. This card is used in game playing as well as in divination. In the first Tarot pack with inscriptions, the 18th-century woodcut Marseilles Tarot, this figure is crowned with the Papal tiara and labelled La Papesse, the Popess, a possible reference to the legend of Pope Joan.
