Her life and career are linked to another artist, the German-Swiss painter Louise Catherine Breslau, of whom she was the companion, the muse and the inspirer.

She met there young artists like her: Anna Klumpke, Hermine David, Agnes Goodsir, Sarah Purser, Marie Bashkirtseff, and especially her "rival", Louise Catherine Breslau.

In 1908, Breslau painted 'La Vie pensive', another work of the couple, now displayed at the Cantonal Museum of Fine Arts in Lausanne.

The two women become an essential couple in the Parisian art scene and receive their artist friends: Henri Fantin-Latour, Auguste Rodin, and Edgar Degas, of whom Zillhardt wrote a biography.

[2] During the First World War, Madeleine Zillhardt distinguished herself in the decorative arts for her "patriotic faience", in support to Clemenceau or denouncing the bombing of civilians, like Fluctuat nec mergitur, Paris bombed, executed in 1918, now part of the collections of the French national Museum of Air and Space.