The Solar Cross may symbolize the 'light of all' which she borrows/reflects, as the Moon does that of the Sun?
(Not sure but the Solar Cross may be from Papus? I seem to recall he makes mention of such.)
“The woman is crowned with a tiara, surmounted by the lunar crescent, she is enveloped in a transparent veil falling over her face. On her breast she bears the solar cross, and upon her knees lies an open book, which she half covers with her mantle.”
The Tarot of the Bohemians
by Papus, p.113
Though more probably both Papus & Waite drew it from Levi:
“It is well known that the hieroglyphic figure on the second Tarot card is still called the female pope, being a woman wearing a tiara on which are the points of the crescent moon, or the horns of Isis. On example in the protestant book is even more remarkable: the hair of the figure is long and scanty; there is a solar cross on the breast; she is seated between the two pillars of Hercules; and behind her flows the ocean, with lotus flowers blooming on the surface of the water.”
The history of magic
by Eliphas Levi, translated by A. E. Waite.
Anyone any idea to which 'protestant book' he is referring too?