After obtaining her baccalauréat at the age of 17, she studied Law first in Marseilles and later in Aix-en-Provence with considerable success. She became a member of the Bar in Marseilles where she practiced for 20 years and was well-known for her exceptional eloquence and efficacy.
Germaine participated in the creation of the first women's unions and helped set up civil rights classes for women. As an ardent suffragist, she joined the Parti Démocrate Populaire (Democratic Popular Party) in 1924 and became a member of its national committee. She became a defense lawyer for children on trial and helped found the Committee for the Protection of Children. In 1936, she married Henri Poinso with whom she had two sons.
During the occupation, Germaine provided shelter and saved the lives of many Jews. She had defended accused "terrorists" of the Vichy Resistance and administered resistance funds for the Socialist Party at the request of Gaston Defferre. At the end of 1944, she joined Marseille's municipal delegation and participated in Resistance activity which led to her arrest by the Gestapo in November 1943.
She was awarded the Resistance Medal and appointed Officer of the Légion d'honneur, Grand Officer of the Order of National Merit, and Commander of the Order of Public Health. A Marseilles Lycée bears her name. She died in Marseille on 20 February 1981.