Garrett earned her Bachelor of Arts in history with special distinction from the University of Oklahoma in 1985. In a 2004 interview, David Levy, Garrett's favorite history professor at the University of Oklahoma, said that Garrett would finish the weekly quiz ahead of the other students and, in the same motion, turn over the paper and reach for next week's reading. Levy also said of Garrett that he "never had a student who made better use of time." As a sophomore at the University of Oklahoma, Garrett became chair of student congress, the University of Oklahoma Student Government Association, a position she held until she graduated.