Ohlfsen was born as Dorothea Ohlfsen-Bagge in Ballarat, Victoria. Her father was Danish, probably born in Schleswig (northern Germany now), and her mother Australian.

She traveled to Germany in 1883 to continue her piano studies; however, when she contracted neuritis, she began teaching music in Germany and later in Russia. She lived in St Petersburg with a Madame Kerbitz and took up painting; she sold one of her work to the Czarina.

Her extentive knowledge of languages gained her employement with the American ambassador and allowed her to write on music, theatre, drama and art for Russian and American newspaper.

After traveling through various Baltic countries, she settled in Rome to study sculpture at the French Academy and with French engraver, Pierre Dautel. She produced many medallions using academic portraits and Symbolyst compositions.

During World War I she became a Red Cross nurse in Italy. The Fascist government were patrons of her work and she produced a large relief portrait medallion of Mussolini and a war memorial, Sacrificio, at Formia, in 1924-26.

Ohlfsen was commissioned by Mussolini to design this memorial because her art studies had been solely in Italy and she had nursed Italian soldiers during the war. This is the only work of its kind in Italy to be made by a woman or a foreigner.

In 1948, she and her companion, the Russian Baroness Hélène de Kuegelgen, were found gassed in her studio in Rome.