Rosa Betje van Oosten was a daughter of Abraham van Oosten and Reina Levie. She married Samuel Lezer in 1898.
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In September 1940, two obituaries were placed in het Nieuw Israëlietisch Weekblad for Rosa Betje Lezer-van Oosten.
Nieuw Israëlietisch Weekblad, 20 September 1940