This is just for scale. I find it weird when you can't tell how big or little something is!
& here is the finished version. Was that background worth all those black pencils I put to rest (3.5 total)? I think so. I think it looks like she was sitting up straight in the middle of the comosition but then relaxed into a more comfortable place a bit off to the side and lower. :-)
I wanted to show what makes a good reference photo for a portrait. Even in high-key lighting you have to have directional lighting that creates shapes of light and darker areas. Usually with high key lighting that means you have one bright main light source coming at an angle and reflected light coming from the other angle to partially light up the shadowed side of the face. You can see below the photograph I used for Shannon's portrait broken down into its value shapes. Even though the shadowed side is light - its still is there to create the illusion of form.
Of course if the eyes are not lit up then I would also suggest not to use the photo no matter how good the lighting pattern. Although I've seen amazing portraits done of people with their eyes in shadow - most people commissioning a portrait want to see the color of the sitter's eyes. As I see it, usually the light in people's eyes are really lit up as in Shannon's portrait (where you see brilliant color), partially lit (meaning not in shadow but you see a bit of color but not vibrant color), and when eyes are in shadow (usually the eyes sockets are even dark). I don't suggest using a photo where the eyes aren't lit and brightening them up yourself, using the rest of the light pattern on the face. The end result will be confusing - somehow your mind knows the lighting isn't right. I would just take another photo (no matter how inconveniet) with the light right to hit the eyes. Practice on yourself with a mirror and a table lamp with the shade taken off to figure out where a good place to place the light to light up the eyes right as well as a good value pattern.