Who is Agatha as noted in the memoir, Aftershocks?

Agatha was Nadia's only black classmate at St. Mary's boarding school in Surrey, England. When Nadia first arrived, Agatha tried befriending her. However, Nadia saw the way the white girls treated her, and began ignoring or actively scorning her. Though she expresses shame over her unkindness towards Agatha, Nadia also understands that her cruelty was a defensive mechanism against the white girls' bullying.