Complex sentence: Irmelin, the elder daughter, studied music theory with her father and in December 1919 married Eggert Møller (1893--1978), a medical doctor who became a professor at the University of Copenhagen and director of the polyclinic at the National Hospital.
Split into simpler sentences: Irmelin, the elder daughter, studied music theory with her father. In December 1919, she married Eggert Møller (1893--1978), a medical doctor who became a professor at the University of Copenhagen and director of the polyclinic at the National Hospital.