When she returned to Chicago, Riley resumed weekly French lessons while rooming on Warren Ave in Chicago. It is here she met her neighbor Dorothy (Jessie) L. Gaynor in 1896. Gaynor started a music class, which Riley joined, and they soon exchanged lessons; Riley taught Gaynor French, while Gaynor taught Riley music composition. Riley made up some lyrics to finish her lesson on lullabies, and Gaynor was so impressed she asked her to write lyrics for a song for her daughter. They quickly began collaborating with Riley's writing lyrics and Gaynor's putting them to music. The songs they collaborated on were mostly for children, finding inspiration from the domestic scene. Their best-known collaboration is called "Slumber Boat", which Gaynor sang in her recital work. Soon, the song received notoriety and they were approached by an agent from John Church Company of Cincinnati, Ohio, who wanted to publish a children's kindergarten book. The resulting book, "Playtime Songs", was very successful all over the United States and in Canada, England, and English schools in Japan. In 1901, Riley got in the habit of having her friend Marie Bartlett over for tea on Thursday afternoons. Initially, she would read while Marie sewed and they discussed current events. Soon other neighbors joined in, and before long, the expanding group was named the Riley Circle. The Riley Circle met at her home in Evanston for many years following the same format, but a lecture given by James O’Donnell Bennett at the Chicago Woman's Club proved critical and changed the Riley Circle agenda from discussing current affairs to reading plays. At the lecture, O’Donnell stressed that Chicago needed to develop an educated audience for drama and the immense influence women could bring toward this goal. Riley credits this lecture for the idea to transform the Riley Circle into the Drama Club of Evanston. The organization was formally founded in 1909, making it the first drama club in the world, according to The Evanston Review, April 24, 1947. In 1929 Riley spent her time between her two residences in Evanston, Illinois, and Pasadena, California, and it was during this time she co-founded the Evanston Art Center. On a trip back to Evanston in September 1929, she outlined the plan for the Arts Center, collaborated with the library board and put through all resolutions and programs. By October 1929, Riley and the Art Center committee had appointed all committee members and planned details for the Art Center opening which was held October 28, 1929, in the center's rooms at the Evanston Public Library.