Who is Bo Morrison from Crow Lake and what is their importance?

Bo is only a baby when her parents are killed. Bo is eighteen months and quickly becomes attached to Luke in the days after the car accident. When Aunt Annie comes to stay with the Morrison children and makes plans to separate them, she tries to separate Bo from Luke, telling Luke that her dependence on him is not going to help her when it is time to leave. However, Luke cannot stand to listen to his sister cry for him. This situation appears to be part of Luke's motivation in deciding to take custody of his siblings instead of going to teacher's college.