In 1901 the family moved to Hampstead in London, where she married Joseph Marguerite Jean-Baptiste Vassal, a physician in the French Colonial Service, in 1903.

[2] Vassal was a keen naturalist and supplied numerous specimens from Vietnam, Gabon and Congo to the Natural History Museum in London for a period of 30 years.

She was considered an unusual collector, first because she was female, and second because she was "operating in French territory and sending specimens to a British museum.

[4] After the outbreak of World War II, the Vassals returned to France and Gabrielle joined the French Resistance.

[6] Vassal authored several books, including a novel titled A Romance of the Western Front published in 1918,[7] On & Off Duty in Annam,[8] In and round Yunnan Fou about her time in Vietnam,[9] Life In French Congo in 1925 and Three Years In Vietnam 1907-1910: Medicine, Chams And Tribesmen In Nhatrang And Surroundings in 1910.