Brigadier General Garrett is a former NROTC student and 1978 graduate of the University of Washington, where she received her BA in English. She was commissioned a Second Lieutenant in the Marine Corps in June 1978. Upon completion of the Basic School, as well as her occupational specialty school, she served on active duty with the 1st Marine Division through June of 1981.

Upon joining the Reserves, BGen Garrett began a long association with 4th Landing Support Battalion (LSB), serving initially as the Battalion S-4A/Maintenance Management Officer in 1981-1984, then Headquarters and Service Company Executive Officer in 1984-1985 and later as the H&S Company Commander in 1986-1988, Battalion S-3/Operations Officer in 1992-1994 and finally as the Battalion Executive Officer in 1995. BGen Garrett also held billets as a Mobilization Operational Readiness Deployment Test (MORDT) inspector and as a member of the Marine Air Ground Task Force (MAGTF) Staff Training Program (MSTP) in Quantico, VA. In 1996, she was appointed by the Secretary of the Navy to the Marine Corps Reserve Policy Board and served as a member for two years. She was in command of 4th LSB from August 1999 until September 2001.

Following that assignment, she served as the Reserve Special Staff Officer for the 12th Marine Corps Recruiting District, responsible for overseeing the Reserve officers and senior enlisted Marines who support the recruiting effort of the eight Recruiting Stations from Seattle to San Diego and Salt Lake City. In October 2002, BGen Garrett took command of the 4th Force Service Support Group (FSSG) Forward (West) at Camp Pendleton. This unit provided battle staff augmentation to the active duty FSSG at IMEF. In November of 2002, she began to serve on active duty with the 1st FSSG. Upon deployment of the Commanding General and his Chief of Staff, from March through June, she served as the Commander, 1st FSSG (Rear). With the return of the Commanding General, BGen Garrett assumed the duties of the Chief of Staff (Rear), 1st FSSG until she was relieved at the end of August. She was released from active duty on September 30, 2003. In July 2004, BGen Garrett was again activated and was assigned as the Chief of Staff, 1st FSSG (Deployed). She served in Iraq from September 2004 through March 2005. She was released from active duty on May 2, 2005 and assumed duties as the Deputy Commander, 4th Marine Logistics Group. Upon activation and deployment of the Commanding General, BGen Garrett assumed the duties as Acting Commanding General, 4th Marine Logistics Group.