She was instrumental in recording old images and saving artifacts in Amsterdam, Netherlands, when occupying Nazi forces threatened their destruction during World War II.

[1][2] In 1934, after the death of her mother in 1934, Bijtelaar began what would become her first masterpiece: drawing copies of all the gravestones in the Oude Kerk (Old Church) and trying to identify the people buried there ("the stone literature of ecclesiastical building history" as she called it).

[2] Another of Bijtelaar's works was mapping and drawing all the bronze bells in Amsterdam after city officials, who were aligned with the occupying forces of Nazi Germany, wanted to remove them during World War II.

[2] She became a member of the Genootschap Amstelodamum (Amsterdamum Society) and wrote a story about "Two glasses with coats of arms of mayors in the Oude Kerk in Amsterdam" in 1949.

Another investigation yielded the exact burial place of Rembrandt's wife Saskia van Uylenburgh (1642), and she laid thirty roses on her grave in her memory.

[2][5] In 1974, woodworker Joop van Huisstede chiseled Bijtelaar's portrait into one of the seat supports in the choir during the restoration of the pews of the Oude Kerk.

[2] On 24 October 1978, two months before her 80th birthday and shortly before the restoration of her beloved Oude Kerk was completed, Bep Bijtelaar died in the hospital that's now called Wilhelmina Gasthuis, but her funeral caused problems.