When Deedra Van Ness answered a call from her daughter, Isabelle, Friday morning, the teen whispered, "Mom, they are shooting up the school, I'm hiding in a closet. I love you mom."
"In the background, I hear gunfire," Van Ness wrote on Facebook Saturday. "I beg her to stay on the phone and she says other kids with her want to call their parents and don't have phones."
Van Ness' heartbreaking post recounts the torturous hours she waited to see Isabelle after a gunman opened fire inside Santa Fe High School in Texas, as well as the emotional and traumatizing toll the experience took on her shy child.
When they were finally reunited and Van Ness took her daughter home, Isabelle opened up about what she experienced, telling her mother the gunman entered her art class from the room next door and started firing.
"Everyone is panicking and running around the room," Van Ness, 50, wrote. "There’s a door at the back of the room to which the kids are running ... only to discover the door is locked and they are trapped. Seeing the kids turning back from the door, she immediately starts running towards items to hide behind."
Isabelle moved "from item to item as the gunman" kept firing, "bullets hitting the walls around her," Van Ness wrote.
"Kids are scrambling trying to hide / escape and she finds an area where he can’t see her, but she can see him," Van Ness said. "She finally runs for the supply closet where she and 6 other kids hide. They are able to lock one door and begin blocking the other door as another girl runs into the closet with them."
The gunman then screamed "Surprise, M*****F******" and started firing into the closet, Van Ness wrote. The gunman hit three of the eight kids there, killing two instantly, she said.
Then, hearing the gunman in the classroom next door yelling "woohoo" as he fired at more students, Isabelle stayed in the closet and called the police, Van Ness said.
The gunman then returned to Isabelle's room, and said to the class, "Are you dead?" as he fired more shots, according to Van Ness' post.
Cellphones were ringing throughout the classroom, and the gunman taunted Isabelle and her classmates in the closet, saying to them, "Do you think it’s for you? Do you want to come answer it?'" Van Ness wrote.
The gunman fired more shots at the closet and tried to get inside, Van Ness wrote.
As Isabelle lay on the ground next to her dead classmates, police arrived outside the classroom and Isabelle listened to the gunman surrender, her mother wrote.
The closet door opened, and with guns pointed at her, Isabelle was told to put her hands up and slowly leave the closet.
The teen walked by bodies in her classroom and hallway before she was frisked and put in a police car to wait for questioning, her mother said.
In Van Ness' post, she also noted moments of kindness, cruelty, fear and despair that affected her daughter in the hours after the shooting.
After she talked to police, a bus driver asked Isabelle whether she knew what happened to her daughter, whom “Isabelle had seen on the floor as she walked through the classroom," Van Ness wrote.
"This wonderful woman did everything she could to make Isabelle feel safe while not knowing the status of her own child," she added.
At home later that day, Isabelle was trolled on social media by other students who blamed her "for not trying to do more to save her classmates, calling her a liar about what happened, etc," Van Ness wrote. "I tell her it’s time to shut off social media and put the phone away."
Isabelle hurried through a shower that day, her mother said, because the sound of "the water hitting the tiles reminded her of sounds she heard while locked in the closet."
And when Isabelle learned the names of all of those killed dead, she "falls apart," her mother wrote. "She had prayed that her friends lying around the school were just injured and the confirmation of their deaths was crushing."
Van Ness also learned that day that her son's best friend was among the dead.
"I now have two children crying and we are helpless and can do nothing but hold them, “Van Ness wrote, “and try to make them feel loved and safe.”
ABC News' Meghan Keneally contributed to this report.