Bieberbach was an inspiring, if unorganised, lecturer and Hanna almost became a geometer. However after the Nazi's came to power in 1933 Hanna became unhappy. She left Berlin University in 1934 to marry Bernhard Neumann, a Jew, so they were forced to leave Germany in 1938, settling in England.
Hanna taught at Hull, then UMIST in Manchester until 1963. The year 1961-62 she spent with Bernhard at the Courant Institute (of New York University) in New York. While they were in New York the invitation arrived for both of them to set up mathematics at the Australian National University. In 1963 Hanna and Bernhard went to Australia where she was to spend the rest of her career.
In 1971 she undertook a lecture tour of Canada. After lecturing in a number of universities Hanna reached Carleton University, Ottawa. There she took ill and died two days later.
Like her husband, Hanna worked in group theory. Her thesis examined free products with amalgamation. Later she worked on varieties of groups and her book Varieties of Groups (1967) is a classic.
A letter from two of her students, published after her death, shows her character:
We will remember her not only as a mathematician, she was a friend who always had a sympathetic ear for any student, and was never too busy. We will always miss her tremendous dedication and sincerity, and the friendliness of her presence.