On the other hand, i think this piece would benefit a great deal from a more interesting palette. This is very nice, but it lacks a certain life that i personally think comes only from mixing and bending light and hue. I would continue to advocate for at least a better color in the shadows than brown (you could pull a Rembrandt and put in a dark green, which would really throw some life into her.
Basically i chose a blueish green because the overall tone of the piece had been red/orange. YOu may want to use a different color, but this is color theory at its most basic; complementary colors used near each other will make a piece more dramatic. it also works for atmospheric perspective if this piece were outside, but something tells me its indoors and so the color of the air is actually the color of the lgihtsource, which is why things tend to look more interesting outside than they do in a windowless room
im rambling. Basically, this is a technically good piece, but it feels lifeless. Having another color will probably help this, though which color you pick is more or less up to you (basic color theory is knowing how to use the rules, advanced color theory is knowing when to break them)