Sweet and three of her girlfriends were being driven home from a birthday party about 1:15 a.m. by the father of one of the girls when they were hit by a Toyota pickup truck driven by 26-year-old Austin Farley.
Sweet's condition is grave. Her family is keeping her on life support so her organs can be donated.
Four others were hurt in the crash and one of Sweet's 15-year-old classmates is in critical condition.
Farley, of Irvine, was booked at the Orange County Jail on suspicion of felony drunken driving and was being held on $100,000 bail.
"He took the life of one of the greatest people I've ever known," said Leah Nawavi, Sweet's friend. "Her last name defines her. She was always sweet. She's going to be missed a lot."
Hundreds gathered Sunday night at Culver Drive and Irvine Boulevard in Irvine, the intersection where the accident took place, for a candlelight vigil.
Northwood High will hold a vigil for Sweet on Tuesday.