Gertrud Marle was born in Vienna as the first of two daughters of the couple Josef Richard and Marianne Marle, who converted from Judaism to Protestantism. Her sister Erika Lilly was born in Prague in 1921. She and Gertrud attended Eugenie Schwarzwald's private reform school. Their mother committed suicide in 1936 and their father died in 1937. Gertrud and Erika Lilly inherited shares in an apartment block located at Piaristengasse 34 in Vienna’s 8th district from their parents.

After the "Anschluss" of Austria to the German Reich, Gertrud and Erika Lilly Marle were among those persecuted and had to submit a declaration of assets, which their aunt Bertha Schiller filled out for the minors. In addition to their share of the house, jewellery, silver and carpets were listed, but no ethnographic objects. On 3 November 1938, the Museum für Völkerkunde (MVK, now the Weltmuseum Wien) received a bow and ten arrows from Brazil as a "gift" from Gertrud Marle and recorded the objects in the entry book under Post II/1938. The inventory was not made until years later. It is doubtful that Gertrud Marle personally brought the objects to the museum, because according to the registration information, she had already been de-registered from the flat of Bertha Schiller and her grandmother Marianne Schiller at Rathausstraße 3/14 in Vienna’s 1st district, to London on 14 October 1938, and her sister Erika followed her on 19 November 1938. An export application submitted by the Popper shipping company on behalf of Gertrud Marle listed works of art and decorative arts, including watercolours, oil paintings, vases and a carpet. The Central Office for the Protection of Monuments authorised the export, but there were no stamps or endorsements to prove that the objects had actually crossed the border. Due to outstanding discriminatory taxes ("Judenvermögensabgabe", JUVA), the Innere Stadt West tax office had liens entered in the land register on the sisters' shares of the property on Piaristengasse that they had inherited from their parents. In 1941, this property was transferred to the German Reich under the 11th Ordinance to the Reich Citizenship Act. As the sisters did not apply for restitution of their shares in the house in Vienna after the end of the National Socialist regime, these were to go to Collection Agencies A and B as heirless assets in 1960.

Gertrud and Erika Lily Marle initially lived on the Isle of Wight after their escape. Gertrud Marle changed her first name to Gertrude and trained as a teacher in England. In 1947, she married George Erwin Blau, who was also born in Vienna in 1911, moved with him to Washington D.C. at the end of the 1940s and became a US citizen. In 1955, her husband got a job as a military historian for the US Department of the Army in Germany. In the 1960s, the family lived in Heidelberg, where Gertrude Marle Blau, who had meanwhile studied German literature, taught German literature and founded a bilingual kindergarten. After George Erwin Blau retired, the couple settled in San Diego, California. In 1999, the now widowed Gertrude Marle Blau moved to Boston. Her sister Erika, who was married to the Brit Brian Pimm, became a singer and pianist and played in the London Philharmonic Orchestra in the 1950s. She committed suicide in 1965. In 2007, the Art Restitution Advisory Board spoke out in favour of the restitution of the ethnographic objects given by Gertrud Marle to the MVK in 1938.