[3] Allen was born on October 23, 1874, in Cameron, Missouri, to David and Pauline Osborn, who were originally from Virginia.

[3] In 1916, under the name Beatrice Osborn Allen, she enrolled at the Lowthorpe School of Landscape Architecture for Women.

Due partly to her late start in her field, her practice remained regional, almost entirely located in New York and New England.

[2][3][4] Allen's landscape designs were influenced by the work of Gertrude Jekyll, whom she met in 1921 on her European travels and whom she would later visit again at Munstead Wood.

In the Carl A. Kroch Library, Cornell University holds a small collection of photographs and plans of her work.