Garrett swerved away from a bicycle in the road, crossed the median and collided with oncoming traffic, according to the Shelby County Reporter.
Alabama State Troopers said the investigation is ongoing at this time.
One other, Ryan Williams of Springfield, La., was injured and taken to an unspecified local hospital, according to the Alabama State Troopers' press release.
Garrett, a junior in industrial and systems engineering, recently completed field training as an Air Force ROTC scholarship cadet.
According to an obituary submitted by Garrett's parents, Garrett was a "young woman with beauty and brawn" who aspired to be a USAF officer.
Other Air Force ROTC cadets and friends will serve as pallbearers while her family gathers for the funeral on July 9 at 4 p.m. at First Baptist Church in Pelham.
She is survived by her parents, Bill and Vivian, and her four sisters, Joan, Ruth, Deborah and Sabrina.