Averianna Patton is thought to be one of the last people the Nashville school shooter messaged before the attack.
On Monday morning, Ms Patton received a message on Instagram from her former classmate, who sounded depressed and desperate.
"She said that I would see her on the news later on… and something tragic was about to happen," Ms Patton told BBC News.
She immediately called the local sheriff's office.
"I don't know what she was battling... but I knew it was a mental thing, you know?" Ms Patton said.
"Just something in my spirit, when she reached out, I just jumped into the mode of trying to call around make sure that I'm doing everything that I could."
But within minutes, Audrey Hale attacked the Covenant School, killing three nine-year-old pupils and three staff members.