What was special about Nadia's relationship with her Aunt Harriet as noted in the memoir, Aftershocks?

Aunt Harriet, Nadia and Yasmeen's aunt, acted as a surrogate mother throughout the sisters' childhood. When Nadia was attending boarding school in England, Aunt Harriet frequently checked in on her, and spent time with her on weekends. Nadia always enjoyed spending time with Aunt Harriet and her children, even adopting their habits and speech mannerisms.