Harriet Ellen Siderowna von Rathlef-Keilmann, (3 January 1887 – 1 May 1933), was a German sculptor and writer of children's books.

[1] She was born to a prominent Jewish family in Riga, Livonia, a province of the Russian Empire.

[2] She married Harald von Rathlef,[1] a lieutenant in the Czarist Regiment of the Alexander Hussars, in 1908 in Riga.

[3] In 1925 she became a major proponent of Anna Anderson's claim to be Grand Duchess Anastasia Nikolaevna of Russia.

[5][6] In Falk Harnack's 1956 film, The Story of Anastasia, she was portrayed by German actress Käthe Braun.