McKelvey developed an interest in landscape design and started volunteering at the
Arnold Arboretum with
Charles Sprague Sargent. Soon, her interest shifted from landscape architecture to botany and she undertook a collecting expedition to Glacier National Park, followed by further fieldwork in the White Mountains in New Hampshire. was published 1928 to great reviews, the first book to receive the Schaffer Medal of the
Pennsylvania Horticultural Society. To date, it is still the only monograph published on the subject. In the same year, she was appointed to the committee to Visit the Arnold Arboretum by the Board of Overseers of Harvard University, a position she held for many years. published nine years apart. published in 1956, was described as her masterpiece and was very well received in the press. Meticulously researched, it examines early expeditions in the Western United States, detailing the specimens collected by explorers including Lewis and Clark and including excerpts of their journals and findings. The book earned her the
New York Botanical Garden's Sarah Gildersleeve Fife award for her literary work. In 1964, McKelvey retired from her positions at the Arboretum and died shortly after on July 11, 1964, in Boston. Her collection of plant specimens and botany research were left to the Arnold Arboretum. McKelvey frequently collaborated with Canadian American botanist
Alice Eastwood, and with other botanists including the Arnold Arboretum's founding member
Charles Sprague Sargent, and
Karl Sax. == Honours ==