[1] Żaneta Hortwitz was born in Warsaw, into a Jewish family, as a daughter of Gustaw Horowitz (1844–1882) and Julia née Kleinmann (1845–1912).

Janina Mortkowicz also translated to Polish Selma Lagerlöf's The Wonderful Adventures of Nils and series about Doctor Dolittle.

During the Holocaust Janina Mortkowicz and her daughter Hanna, were hiding at the Aryan's side of Warsaw.

[2] Janina Horwitz died on 27 December 1960 and was buried at the Rakowicki Cemetery in Kraków.

[citation needed] Her daughter, Hanna Mortkowicz-Olczakowa was a famous writer, her granddaughter Joanna Olczak-Ronikier is also a writer and her great-granddaughter Katarzyna Zimmerer is a journalist.