Video footage of the incident, which was uploaded to social media and has since been widely shared, allegedly shows two of the girls punching, kicking and banging the victim's head into a wall inside a parenting room in Figtree Grove as a third teen films the encounter.

The defenceless victim can be heard screaming in pain and yelling "please stop, you're going to kill me" before she begins to convulse.

The trio, none of whom can be publicly identified for legal reasons, allegedly smashed the victim's phone and threw it into the toilet before fleeing the scene, leaving the victim alone on the floor.

Police prosecutor Sergeant Seleena Gilmore said Wollongong and Lake Illawarra police were subsequently "inundated" with reports of the incident by concerned members of the public who provided them with copies of the footage after it was uploaded to social media.

Officers arrested the three teens - two 15-year-olds and another aged 17 - on Sunday and charged them with an aggravated kidnapping charge, which carries a maximum sentence of 25 years' jail.

One of the teens was also charged with common assault over a second incident at Woonona Railway Station a few weeks earlier, in which she allegedly grabbed hold of the same victim and pushed her onto the train tracks.

All three girls faced Port Kembla Children's Court on Monday but that teen was the only one who sought release on bail.

She sobbed throughout most of the proceedings as defence lawyer Jack Hibbard said she had no prior criminal history and would agree not to contact the victim or her co-accused if released on bail.

"She understands the seriousness of the charges against her," he said.

"She's spent her first night in juvenile detention and is upset and desperately wants to get out."

Sgt Gilmore opposed the girl's release, labelling her actions "vicious and premeditated".

She claimed one of the girls had lured the victim to the location while the other two lay in wait behind a curtain inside the room.

Arresting officers were also scathing of what they witnessed on the video, claiming the victim lay "defenceless on the ground" as the trio "attacked her like a pack of wild dogs".

"The [accused] have conducted a vicious attack on the victim that has lasted an extended period, where the victim pleaded with the [accused] to be allowed to leave," officers wrote in a set of fact sheets tendered to the court.

"[They] showed no remorse and continually kicked, stomped on and threw the victim's head into a wall.

"Police have no idea how the victim does not have more serious injuries."

Magistrate David Williams refused to release the teen, noting the case against her appeared to be a very strong one.

"This young person lay in wait for the complainant who, by some deception, was taken into an area away from the public and in essence ambushed.

"It was a sustained and damaging assault.... [with] a high degree of criminality."

All three cases were adjourned to June 30 for police to serve the brief of evidence on each girl's legal teams.

Meanwhile, the 17-year-old is expected to apply for bail in court on Tuesday.