She was born in Mannheim, the daughter of Johann Otto Stamm, a government secretary, and Sophia Elisabeth Wimmer.

[1] She married Franz Fridolin Weber [de] (1733–1779) on 14 September 1756, and had four daughters: Josepha, Aloysia, Constanze, and Sophie.

[2] He fell in love with her daughter Aloysia during this stay and departed for Paris after finding no permanent position in Mannheim.

In 1781, he settled in Vienna, hoping to pursue his career there, and on 1 or 2 May 1781, he became a boarder in their home (in a building called Zum Auge Gottes, "God's Eye").

[4] Cäcilia asked Mozart to move out when she realized that he had fallen in love with Constanze, for the sake of propriety.