At what point does Julie's relationship with her older sister, Laura, change in the novel, Up a Road Slowly?

Laura, Julie's older sister, was seventeen at the time of her mother's death and allowed to stay with her father to finish high school, because she does not require much daily care. Julie sees Laura as a heroine with the most feminine qualities, and their relationship is very close in spite of their living in different homes. Their relationship, however, changes when Laura marries, and Julie feels that she is not as important in her sister's life. However, when Laura names her daughter Julie, the sisters' relationship is cemented. Laura takes on the role of advisor for Julie during her school years, and it is Laura, whom Julie would most like to emulate.