Senator Mosley comes from a family of public servants who have all served in the Missouri House of Representatives, beginning with her father, Elbert Walton Jr., who served from 1979 to 1992. Her late stepmother, Juanita Head Walton, served from 2001-2008, and her sister, Rochelle Walton Gray, served from 2009-2016. Her brother-in-law, Alan Gray, and her husband, Jermond (Jay) Mosley, are currently serving in the House after first taking office in 2017. Senator Mosley and her husband, Rep. Jay Mosley, are the first and only married couple to serve in the Missouri Legislature at the same time.

Senator Mosley is a native St. Louisan. She attended St. Louis Public Schools, attending Central Visual and Performing Arts elementary and high schools. She received an associate certificate from Florissant Valley Community College and graduated from Grambling State University where she received a Bachelor of Arts in recreation. She has been employed by AT&T for over 20 years and serves as a steward with the Communication Workers of America, Local 6300. She and her husband attend Influence Church, and they have three children, Chanel, Janay and Jermond II, and one granddaughter, Navi.