That has never been determined precisely. The "window" is that she was ultimately sent to Theresinstadt, and died either en route, or shortly after arriving there in the last days of the war.
The most specific answer that can be given to this question is "Sometime between late February and mid-April of 1945". Early to mid-March is most likely. It is not even known for certain where she died - whether in Theresinstadt, or en route to there.
Mrs. van Pels, whose full name was Auguste van Pels, died in either April or early May 1945 in the Bergen-Belsen concentration camp.
Mrs. van Pels, aka Mrs. van Daan in Anne's diary, was aged 44. it's unknown whether she died in April or May of 1945
That is Mrs. Van Pels real name. Anne Frank used Mrs. Van Daan in her diary.
She is belived to have died on a death march of prisoners to some camp called Terezin in Czecheslovakia or shortly after arriving there.
Auguste van Pels (Mrs. van Pels).
Mr. van Pels accepted it fairly good-naturedly, while Mrs. van Pels was a bit of a prima Donna and complainer about many aspects of it.
Mr. van Dann: Hermann van Pels and Mrs. van Daan: Auguste van Pels
Auguste van Pels went by Petronella van Daan, Kerli, Gusti, and Mrs. Beaverbrook.
Peter van Pels/van Daan.
Fritz Pfeffer Patter van Pels Mr. van Pels Mrs. van Pels Edith Frank Otto Frank Anne Frank Margot Frank
Mr. Van Pels, Mrs. Van Pels, Peter Van Pels, Margot Frank, Edith Frank, Otto Frank and a dentist friend.
Peter van Pels died of exhaustion after a death march from Auschwitz to Mauthausen.
Mrs. Van Pels, also known as Auguste van Pels, was described in Anne Frank's diary as petite, elegant, and having a round face with dark eyes and hair. She was a fashionable woman who often dressed well even in difficult circumstances.
In the afterword of The Diary of a Young Girl by Anne Frank, Mrs. van Pels was taken away with Anne and Margot to Belsen. Mrs. van Pels died at Belsen, but no witness marked the date. I hope this information was helpful. -22redroses