Catrina Alexander, of Mount Airy, said she knew something was wrong when her 17-year-old daughter, Macy Smith, missed her curfew.
She tracked her using the "Find My Friends" app and found Macy pinned under her car after she fell down a 25-foot embankment.
"I can't explain watching the GPS on my phone -- my dot for my phone getting close to hers and then suddenly seeing the tire tracks, and that's all I could see," Alexander said.
Smith told WFMY-TV that her car hydroplaned before flipping over and rolling three times.
Both mother and daughter are encouraging others to download the tracking technology in case of an emergency.