Who is Shelby Wakeman from Second Glance: A Novel and what is their importance?

Shelby Wakeman is Ross's sister. She is described as a middle-aged, divorcee and librarian, who lives her life in darkness because her son has a rare medical condition in which he is allergic to UV light. Shelby's life revolves around her son, and she refuses to believe that he is destined to die before he becomes an adult, as a result of his rare disorder. When Shelby meets Eli Rochert, a police detective, she comes to realize that she cannot live her life waiting for the worst to happen.