 Mosheim became established under Max Reinhardt, and in 1925 he gave her the chance to substitute in the play "Der sprechende Affe" by René Fauchois when the female lead became ill. Mosheim learned the difficult role from Albert Bassermann in just 24 hours and became a superstar almost overnight.Until 1933, when she went to London to escape Adolf Hitler's rise to power, she was pre-eminent in the Berlin theatre scene.She performed in a wide variety of roles, being equally at home in drama and comedy.