Lenski's first professional goal was to become a painter. Her oil paintings were shown at the Weyhe Gallery in New York in 1927 and her watercolors were shown at the Ferargils Gallery in New York in 1932. During this period she also worked as an illustrator, beginning with jobs she took to support herself while studying at the Art Students League between 1915 and 1920. Her first publication was a coloring book called "A Children's Frieze Book: To-Put-Together for Home Decoration" (1918), for which she was paid $100. She also produced three books of paper dolls for the same publisher, Platt and Munk, during 1918 and 1919. In 1920 Lenski chose to study in London in part because it was the longstanding center of children's book publishing, a field in which American educators, publishers and librarians began to engage seriously only after World War I. In London she illustrated three children's books for the publisher John Lane, including new editions of two stories by "Wind in the Willows" author Kenneth Grahame. After returning to the United States she continued to work as an illustrator, focusing primarily on collections of folktales and fairy tales during the 1920s. Among the first books for which she provided text as well as illustrations was a collection of nursery rhymes.