Daniel-Lesueur integrated the Société des Gens de Lettres in 1892, and in 1990 applied for entering the Committee. She failed, but tried again – successfully – in 1907, and became consequently the first woman to be elected at this Committee. George Sand had indeed been co-opted but never took part in any meeting of the Bureau, and did not come to the General meetings.
Daniel-Lesueur was not only seating in the Committee, but was also willing to take operational responsibilities. She became Secretary immediately (between 1907 and 1908). The members appreciated her interventions and her efficiency as well, and chose her as Vice-President (1908-1910). In 1911 she was re-elected at the Committee for 3 years, and was Vice-President again (1913-1914). She was founding member of the Gens de Lettres Trade Union from 1918 until her death.
In 1913 she enthusiastically participated to the creation of the Denier des veuves de la Société des Gens de Lettres, a charity. Motivated by her patriotic fervour, she created with friends the Aide aux Femmes Combattantes as early as August, 9th 1914, and she was an active contributor of the Croisade des Femmes françaises in 1915 (she was President from 1916). From July 1918 she worked directly in a foster home for soldiers. She is the godmother of a female hero of the war: Marcelle Semmer.