Who is Mrs. Murdo from The City of Ember and what is their importance?

Mrs. Murdo is Granny's neighbor. She cares for Poppy when Lina's Granny isn't feeling well, and after Granny's death, she takes Poppy and Lina in to live with her. Mrs. Murdo is described as a very organized woman, who takes great pride in keeping her apartment neat. She also takes pride in caring for the girls.