Premise: Alma Rosé's father was the violinist Arnold Rosé (né Rosenblum; 1863–1946) who was the leader of the Vienna Philharmonic Orchestra for 50 years: from 1881-1931 as well as leader of the Vienna State Opera orchestra and leader of the legendary Rosé String Quartet. Her mother, Justine (died 22 August 1938), was Gustav Mahler's sister. Alma was named for Alma Mahler.
Hypothesis: The Rose family changed their name from Rosenblum due to immigration.