With spot illustrations, the light source can come from wherever I want it to. As another spot, therefore, this one should have been no different. But this drawing also happens to be part of a sequence, and the D page illustration as well as the G have the light coming from the upper left hand side.
So unless I was imagining that the ball would drop out of her hand and reverse direction once hitting the ground, I had to have the sun to Arianna's back in this picture. Normally, I like to highlight a face by, well, highlighting it. But now I had to draw attention to the face with shadows. It seems to work out – the face has the greatest value contrast, so the eye (or my eye, anyway) goes straight there.