Who is Mama Jean from Somewhere in the Darkness and what is their importance?

Mama Jean is a middle aged woman who babysits for a living. Mama Jean is a family friend of the Littles and has taken custody of Jimmy since he was a small child. When Crab arrives at their apartment and demands that he be allowed to take Jimmy, Mama Jean does not fight him. However, it is clear to the reader that Mama Jean does not want Jimmy to go. In fact, Mama Jean takes each opportunity she has to reassure Jimmy he can always come back to her if he wants.