"She was going to be a star," he said Thursday.
James was a head coach of the varsity basketball team at Walnut High School and coached her during her freshman and sophomore years there.
"The big thing with freshmen was they're scared and she had not fear," James said.
Authorities were searching for former LAPD officer Christopher Dorner in connection to the killings of Quan and 27-year-old Keith Lawrence. The couple was found shot to death in their car at Sunday night.
Quan's freshman year saw her as the only freshman on the team. There were a few sophomores and a few juniors but the team consisted primarily of seniors, he said.
She was had the ability to remain calm under pressure. During one game Walnut was playing against an Alhambra-based high school. Quan knew of number of students.
"Some of the fans were on her and it didn't bother her at all," James said.
Quan wasn't just a good basketball player she was also a a carrying person who was well liked by those who knew her.
"She never changed. She was always positive," said James who remained in contact with her as she went on to college and and became a coach herself.
After Quan became a coach James tried to get her to become a coach at Diamond Ranch.
In addition to her talent as an athlete Quan had something else.
"Monica was a student of the game," James said.
The ability to remain calm was something she carried into her coaching career.
"She had a very calm demeanor ... A lot of players need that," he said.
James and his Diamond Ranch coaching staff, which also knew or coached Quan, attended a vigil that was organized Monday night at Walnut High.
"Almost every kid who she played with was there," James said. "That shows me there is a bond and respect there."
"I feel so bad for her mom and her dad," he said. "She was everything to them."
Quan's parents were frequently at practice and they never missed a game.
The Quans had two children, Monica and an older son.