Erna was born April 1, 1892, in Gross Rheide, Schleswig-Holstein, Germany. Her parents were Heinrich Frees and Maria Catharina Margaretha (Tiedemann) Frees. She immigrated to the United States at the age of six with her parents and her brother Juergen Hinrich Frees and sister Maria Magdalena. The family immigrated on the ship Auguste Victoria and arrived in New York on August 5, 1898.

Erna married John Kruse, Jr, the son of John J. Kruse and Dora Eichman. She died on March 14, 1918, at the age of 25 in Manning, Carroll County, Iowa.