A 3-year-old child was caught in the attack and could have been seriously injured.
The 14-year-old victim was reportedly babysitting the child, who is her niece, during the incident.
A video clip of the attack was reportedly first posted on YouTube on Tuesday. It shows two young females demand that another girl "get up." She is holding the young child and refuses.
The aggressor then pulls the girl up by her hair and the child falls to the ground. The child can be heard crying while the girl is dragged off and beaten.
The victim went to school with the suspect, but they only knew each other in passing. Police say the two had a minor altercation during the school year, but nothing major.
Investigators believe the teens just happened to cross paths at a playground at Herfurth Elementary School in Rowlett, where the video was recorded.
The original video has since been removed from YouTube, but copies of it still exist on LiveLeak and Facebook.
Rowlett police say the June 19 attack was pre-mediated.