Vicious Morgan Findlay pulled her victim’s hair from her head.
She and a gang of others left the girl with blood on her face, crying and shaking from the unprovoked attack.
The now 18-year-old pleaded guilty and has been locked up to await sentencing.
Dumbarton Sheriff Court heard how Findlay, of Panmure Street, Possilpark, was on the 5.13pm train from Airdrie to Balloch with a group of female youths on May 7 last year.
Around 6.25pm, a 15-year-old girl boarded and walked into the carriage where the group was sitting.
As she passed through, Findlay grabbed her arm, “as if in an attempt to make her dance,” said the prosecutor.
The youngster didn’t engage and entered another carriage, sitting down alone.
But the accused and her gang got up and followed her.
CCTV captured Findlay approaching, starting to engage with the seated youngster. The other girls appeared to join in the argument.
Findlay, then aged 17, took the girl’s mobile phone from the table in front of her. And the rest of the gang started to record what happened on their phones.
The 15-year-old stood up to try to regain her phone, only for it to be thrown on the seats.
Her attacker lunged at her, grabbing the girl’s head and punching her multiple times.
The girl fell to the floor, lying in the aisle of the carriage as they all punched, stamped and kicked their victim on the head and body.
An unknown man approached and tried to stop the attack.
Findlay gestured along the carriage to another female, who ran into the carriage and pushed the man.
The assault continued as the girl was repeatedly punched and kicked. Then they dragged her by the hair to the space near the train doors.
They continued the attack for about 4.5 minutes until the next stop, where they left.
The girl was found with extensive bruising and attended hospital, but no fractures or other injuries were found.
Police later traced the attacker.
She told them, “I didn’t steal her phone” and “I don’t know her.”
On May 26, Findlay pleaded guilty to the assault, with others, between Renton and Balloch stations.
She lunged at her, seized her by the body, repeatedly struck her to the head causing her to fall, repeatedly struck, kicked and stamped on her to the head and body, dragging her by the hair, pulling the hair from her head.
It was all to the girl’s injury and the danger of life.
She was on bail from Glasgow Sheriff Court.
Sheriff John McElroy KC revoked her bail and remanded her in custody until sentencing, set for June 16.
