Maybe a bit of lighting? There would be some interesting stuff going on since she's sitting near a window. Nothing too fancy. I think some sort of texture instead of flat color could add interest, you've already got it going in the wallpaper in the background. Maybe Some sort of pattern in her dress... wood grain on her rocking chair... maybe drop shadows to give stuff a layered cut paper look. Hope that helps.
Hmm, I agree with Sean. I'm missing your trademark textures in this one - the floor looks fantastic but maybe some pattern on her would help too.