Smudging is another way to create depth. By smoothing out the skin tones, we effectively separate it from the hair.
Try smudging along the face lines with your finger to blend them into the surrounding areas. Also try smudging from the nose area leftward towards the edge of her cheek. You will practically sculpt the cheek bone and sinus area with your finger. Don't forget under the eyes since that detail attributes to the resemblance of your drawing to your model.