The incident was captured on video outside Primos Elementary School Sunday afternoon. The video was released by police Wednesday.
Police say mom is 45-year-old Michele Davenport.
In the video, the girls seem reluctant. But Davenport has them square off and start swinging. She can be heard yelling instructions from the sidelines.
After awhile the girls get tired of the struggle and actually try to shake hands. But mom signals round two.
Police say Davenport claimed her daughter had been bullied and she came to help her settle a score.
"Mom still does not believe this is a big deal. She can't understand why she was arrested," said Upper Darby Police Superintendent Michael Chitwood.
Davenport and her daughter have both been arrested.
The victim was treated at the hospital for a concussion and other injuries.
Police say they have zero tolerance for this kind of thing, especially since the recent death of 12-year-old Bailey O'Neill in nearby Darby Township.
He fell into a coma after a schoolyard fight and died two weeks ago.
Both Bailey and the victim in this case were classmates at Darby Township Elementary School. She was an altar server at his funeral.
The police say it's tough to send home the anti-bullying message when parents act like this.
"Mom's teaching the kids the wrong thing," said Chitwood. "Mom acted like a moron."
The daughter was released to the custody of her father last night.
Davenport spent the night in jail and is now free on ten percent of $35,000 bail.