Molkenboer was born in Weesp in 1883, one of fourteen children of the sculptor and painter Willem Molkenboer and Maria Cecilia Petronella Johanna Derkinderen.^[2] She was a sister of the painters Antoon and Theo Molkenboer^[3] and of the literary scientist Bernard Molkenboer.^[4]

She attended the Rijksnormaalschool voor Teekenonderwijzers, an art school founded by her father, from 1900 to 1905, followed by a year at the Rijksakademie art school.^[5] She became an art teacher and worked as one at least until 1930.^[1] Between 1916 and 1920 she was involved with the magazine Jong Leven and she became a member and later secretary of the catholic art society Kunstkring de Violier in Amsterdam.^[1][6]

In 1907 Molkenboer produced drawings for a book by Johanna Naber, followed by some book covers, mostly in Art Nouveau style.^[1] She worked with the toy factory Olanda, designing wooden toys and children's furniture.^[1] In 1924, at the occasion of the 27th Eucharistic Congress, Molkenboer designed commemorative plates for De Koninklijke Porceleyne Fles in Delft.^[5] She also did some occasion work for the earthenware factory De Sphinx in Maastricht.^[7] Some of Molkenboer's work was distinguished at the Panama–California Exposition in San Diego.^[1]

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  Sheet music cover, 1898 coronation song
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  Book cover for Marie Koenen, 1938
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  Memorial plate, Kingdom of the Netherlands 100 years, 1913
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  Memorial plate for the 27th Eucharistic Congress, Amsterdam, 22–27 July 1924