Returning to Chicago, she continued to organize women and successfully lobbied for a state factory law regulating the employment of women and children. After its passage, she became a deputy to Chief Inspector Florence Kelley.
In 1894 Kenney married John O'Sullivan. They lived in Boston, and over the years she wrote articles for the Boston Globe on women, trade unions, and labor issues. She continued to organize women workers with the support of the Women's Educational and Industrial Union and also helped found and served as executive secretary of the Union for Industrial Progress, a group studying factory conditions.
At the 1903 AFL convention she was one of the founders of the Woman's Trade Union League (from 1907, the National Women's Trade Union League, serving as its first secretary (1903) and later as its vice-president (1907-9); she resigned from the NWTUL in 1912. In 1914 she became a factory inspector for the Massachusetts Department of Labor and Industries, holding that post until her retirement in 1934.