Bertha (Betty) Bloemendal was a classmate of Anne Frank in the period 1941-1942 on the Jewish Lyceum. On 15 June 1942 Anne Frank writes about Betty in her diary. Betty was also present at her birthday party. On 21 September 1942 Anne writes that she heard Betty was deported to Poland.
See also: B. Polak, Naar buiten, lucht en lachen (Amsterdam 2006) 152.