Born in New York, on Manhattan Island, Justine moved to London with her parents when she was six. She returned to the USA for regular visits, some of which involved seeing her grandmother’s Cousin Daisy, who lived in Wilderstein on the Hudson River. 

Her award-winning debut novel, Daisy Chain, is the fictionalised tale of Daisy Suckley's affair with FDR and the complicated web of women who surrounded and influenced him. The author has used some conventional research, but she also included previously unknown family secrets.