Kristen Stewart could be a sweet face to look at and admire but when it comes to drawing, she is quite a tough bet. It is quite hard to bring the innocence that she somehow manages to have always.
Take a look at her. It is quite not defined but yet good for her face. Look at her nose. She has a beautiful round nose-tip which looks quite flat sometime and this reference has the nose quite protruded on the right. It took extreme concentration to pull that out.