Rosa Rein was born in a prosperous Jewish family in Dzietzkowitz in the eastern part of the German Empire. Presently, the place of her birth is Dziećkowice, a distict of Mysłowice, Silesia Voivodeship, Poland.
Rein was married in 1935. She and her first husband, a German, emigrated to Brazil in 1938 as life for Jews became impossible in Nazi-ruled Germany. Rein’s husband died not long after they arrived in Brazil, and she remarried in 1949. She and her second husband moved to Paradiso on the outskirts of Lugano in 1964 for health reasons. She remarried for a second time in 1973.
Rein had no children and her mother died in a German concentration camp.
Rein was in good health. In 2001, at the age of 104, she moved to a nursing home in Lugano, Ticino, Switzerland. Rein died there on 14 February 2010 at the age of 112 years, 327 days. At the time of her death, she was the 14th-oldest living person and 4th-oldest living European.