In 1893, along with Auguste Fickert and Rosa Mayreder, she founded the Allgemeiner Österreichischer Frauenverein (General Austrian Women's Association).

In 1902, Lang attended the International Abolitionist Federation's conference in London and visited the Passmore Edwards Settlement, becoming an advocate of social welfare programs.

Joining the Committee on Woman Suffrage in 1905, she worked actively to change Section 30 and gain women's voting rights.

The Settlement Society she founded remained in operation until 2003 and pioneered many social services in Austria, such as adult education, child and maternity care, summer camp programs, and tuberculosis treatment.

[9] They also summered with a colony of friends in Grinzing at the Schloß Belle Vue,[3] known as the place where Sigmund Freud experienced his dream, Irma's injection.

[12] Steiner commented that Lang was the soul of the circle, and that it was her personality and interest in theosophy that encouraged the participation of group members with widely differing views.

[4][15][16] More similar to organizations developed for workers than middle- and upper-class women's groups, which focused on charity, the Frauenverein supported working class rights to employment, education and legal protection for the poor, and the abolition of laws regulating prostitution.

[23] Lang compared the works of architects like Adolf Loos and Joseph Maria Olbrich; musicians like Gustav Mahler; painters such as Klimt; and set designers like Alfred Roller as expressions of freedom to feminists' rejection of patriarchy.

[24] In 1898, along with Fickert and Mayreder, Lang co-founded [16][25] Dokumente der Frauen (Women's Documents), as the press organ of the Frauenverein to echo the artistic revolution of the Secessionists.

The first project of the Settlement Society was a school kitchen they operated in Brigittenau, though they were unable to locate a suitable building for housing.

Without ties to political or religious affiliations, for a small fee workers could benefit from health care for pregnant women and for children, a nursery for childcare for working mothers, mixed-gender education, classes on cooking, and social evenings with musical performances or lectures.

[32] That year, Lang's son Heinz committed suicide after a failed love affair with Lina Loos, wife of Adolf.

Arthur Schnitzler wrote a play, Das Wort (The Word) based on the tragic events, which led to Heinz's death.

[34] Lang represented the Committee as Austria's delegate to the 1908 International Woman Suffrage Alliance 4th congress held in Amsterdam and gave a report on their activities.

[36] During World War I, Lang worked in the military hospital set up in the Akademisches Gymnasium, performing Swedish massage therapy.

The couple's sons Heinz von Foerster became a noted a physicist in the United States and Uzzi Förster [de] was a musician who introduced jazz to Austria.

Lilith left her family papers, which are protected by the Federal Monuments Office, to the Wiener Privatbesitz (Viennese Private Collection).