In my reference photo, the model had the majority of her face in shadow and I thought it would be an interesting challenge to render the shapes. I ended up creating a lost edge between her face and the hair, but found that creating a small temperature difference (warm in the face and cold in the shadows) provided enough information to get the features to read better. I then played with the hair and background -- pushing and pulling each -- until I found a balance that I felt was effective in creating a mood.
Here are a few progress shots. The outline was painted with a combination of red oxide, ultramarine blue, and alizarin crimson. In the second shot, I had the face more rendered than the final painting, but found it distracting, and ended up scumbling it out to create a lost edge with minimal detail.