Step 16: Add Barbie's bottom lip by darkening the path of the guide. Draw a similar curved line above it as the mouth opening.
Step 17: Darken the initial U-shaped line under the circle to create Barbie's chin and jaw. Don't darken the line above the horizontal construction line because that will be covered by Barbie's hair.
Step 18: Darken the lines under Barbie's head to for the neck and top part of the shoulders. Notice how the neck lines overlap the shoulder lines a bit.
Step 19: Barbie's hair can be a little tricky too, so it's also divide into two parts. Use the initial curved line over the head as a guide to draw the right side of the hair. Darken the right side of the line, but then curve it in toward the forehead and then back out to the right side of the face. It's okay if it overlaps Barbie's eyebrow and ear.
Step 20: Now draw the left side of Barbie's hair by darkening that side of the guide. Add another curved line closer to the face that overlaps the ear for the front part of the hair.