It occurred to me that the main thing Waite may have been trying to symbolize in this card is the
idea of Shekinah. He mentions Shekinah and the fact that in the Zohar there are two Shekinahs, one above and one below. I think this may account for his apparent contradictions in his description (i.e. saying she's the moon nourished by the milk of the Supernal Mother but also saying she's the Supernal Mother herself); it would also help explain the meaning of that yellow crescent at her feet. He incorporated aspects of both Shekinahs into the image. Both are represented symbolically by the moon but each have different meanings.
The face in the bright yellow moon on the Moon card is Shekinah below. In the
Pictorial Key Waite describes it as "the face of mind"; but in his description of the Great Symbol of the Moon (which incidentally is exactly like the RWS Moon in all its essential elements) for the Fellowship of the Rosy Cross, he makes clear it's Shekinah:
"The Symbol of the 28th path represents Shekinah as the new Moon on the side of Mercy, looking towards the glorious Sun of Tiphereth and reflecting its sacred radiance. The animals below are the unregenerate instincts of the natural man in Malkuth, while the crayfish reaching up toward the land is the evil part of our nature. Shekinah is the soul-part shining in the region of material darkness, ignorance and savage fear. She reflects over the sad region of our suffering estate the Divine Light of the Self-Knowing Spirit."