Abrac
I think the Empress is also the woman clothed with the sun. From the PKT: "There are also certain aspects in which she has been correctly described as desire and the wings thereof, as the woman clothed with the sun. . ."
She is the mother that becomes the bride, the bride being the Empress. She is also Hathor or Mehet-Weret, carrying the sun disc between her horns. She is associated with water and the flooding of the Nile, so that links her with Sirius.
https://en.wikipedia.org/wiki/Hathor
https://en.wikipedia.org/wiki/Mehet-Weret
I would still like to know why the crescent moon is placed at her feet. We know the Moon card is Pisces, and Pisces is the feet, is that the only connection?
P.F. Case considered it more appropriate for the crescent moon to be under the foot of the Empress rather than the High Priestess. I forget his reasoning.
Anyhow, there are occasional posts from neo pagans who are dismayed by the negativity of Trump XVIII. Apparently they are not taking Trump II into consideration. Of course, a lunar goddess should have destructive as well as creative powers, so it is appropriate for her to have both negative and positive cards.
Isaiah 45:7 King James Version:
I form the light, and create darkness: I make peace, and create evil: I the Lord do all these things.
So I'm not sure why a few posters have tried to relate the HP back to the Moon tarot card, though I can see the connection.....