Who is Hannah from Autobiography of a Face and what is their importance?

Hannah is the cleaning lady in Dr. Woolf's office. Lucy sits with Hannah after her chemo each week, while her mother goes to get the car. Hannah always offers Lucy a cup of tea, and when Lucy tells Hannah that her nose hurts..... Hannah is the only one who believes her. On the day of Lucy's final treatment, she cries and Hannah does make her a cup of tea.