A 15-year-old girl accused of beating a former friend on a western Sydney playground said she is "not sorry" for what she did — only the way she did it.

In the video, believed to have taken place in a Cranebrook playground, a gang of teenage bullies surround their victim, who is pushing an infant on a swing.

She insists she doesn't want trouble and tries to reason with her assailants.

"Can't you just take no for an answer? I am not fighting you right now," she said.

"And I have never had a fight in my life."

One of her tormentors says, "Well, it's time to experience them."

The victim tries to walk home but is followed and cornered.

Her attacker has her by the hair and lays into her, knocking her to the ground after kneeing her repeatedly in the head.

There is one final kick to the face and then the victim lies motionless on the ground.

The accused attacker told 9News she was not sorry for what she had done but for how she had done it.

"I'm sorry for — I don't regret what I done, only for the way I did it," she told 9News.

"I didn't mean to hurt her the way I did, and all that stuff."

The 15-year-old accused was formally charged with the assault today and has been placed on strict bail conditions.