Harriet Ellen Siderowna Keilmann was born to a wealthy Jewish family in Riga, Livonia (now Latvia), then a province of the Russian Empire. She took private art lessons as a child and by the age of 21 had exhibited her work in the Baltic Art Society in Riga. From 1906 to 1908, she studied at art schools in Berlin and Munich. In 1908, she married Harald von Rathlef, an officer of hussars in the Tsarist army, with whom she had four children. After the marriage, she was known as Harriet von Rathlef-Keilmann. The family fled the Bolshevik Revolution to Germany in 1918. She divorced her husband in 1922 and made a living with her sculpture and writing and illustrating children's books.
She enrolled at the Weimar Academy of Fine Art and later briefly at the Bauhaus in Weimar. In Berlin, she befriended Anna Anderson and supported her claim to be the missing Grand Duchess Anastasia of Russia, writing a series of articles about her. Although highly regarded, she was forced to resign from the Society of Berlin Women Artists with the rise of the Nazi regime. She was hoping to leave Germany when she died of complications following a burst appendix in 1933 at age 46.