I always keep the original sketch scan file when I go to make line art, so I can redraw something if it seems off. As for that sort of shading, it would essentially invert the light and dark, making the light creep over the edges and the darker shading dominate the body, while using a different light source to show her face and other key points of the art. Not only does this create a seductive tone for the piece, but it also shows a sort of diamond in the rough characteristic for the main attraction.
By weightless I mean that an alicorn is fairly large, and her wings are quite big as well. The weight of the body should show pressure of the hooves on the ground, however this does not, you drew her to look practically weightless, while this concept is great for otherworld creatures, spirits, and goddesses, Weight can drag the art down if not used correctly.
This piece does well to show the character to be a graceful yet powerful pony, and the hair as well as the setting compliment the body and face.