Harriet Ellen Siderowna von Rathlef-Keilmann, (3 January 1887 – 1 May 1933), was a German sculptor and writer of children's books.
Keilmann was born to a prominent Jewish family in Riga, Livonia, a province of the Russian Empire. In 1908 she married in Riga Harald von Rathlef, a lieutenant in the Czarist Regiment of the Alexander Hussars. The couple had four children. The family escaped revolutionary Russia from Riga to Berlin on Dec. 28, 1918. She divorced her husband in 1922 and supported her children with the income from her sculptures, graphics and illustrations.
In 1925 Rathlef became a major proponent of Anna Anderson's claim to be Grand Duchess Anastasia Nikolaevna of Russia. She befriended the claimant and wrote a series of articles about her. In the same year she converted to Roman Catholicism.
Rathlef, who was involved in artistic circles and social causes in Berlin, was forced to resign from the Society of Berlin Women Artists when Adolf Hitler rose to power. Alarmed by the political developments in Nazi Germany, Rathlef hoped to leave the country. Before she could make definite plans, Rathlef died in Berlin on 1 May 1933 of a burst appendix.
In Falk Harnack's 1956 film, The Story of Anastasia, Rathlef-Keilmann was portrayed by German actress Käthe Braun.