The footage shows the woman on a park bench, grabbing the child's hair, then pushing her forward.
The Los Angeles County Sheriff's Department's Special Victims Unit is now investigating.
RELATED: Daycare worker seen on video hitting, shaking kids charged with child abuse
The woman who shot the video, Evette Jones, told Eyewitness News the incident happened Friday afternoon at Tierra Bonita Park.
"This child can't stand up for herself. She can't let her mom know what happened to her," Jones said as she held back tears.
Sheriff's officials said the mother of the 9-year-old child reported the incident on Sunday. Initial information from the investigation indicates that the woman seen striking the child in the video is the daycare provider of the child.
With tears, Jones said she's since spoken to the girl's mother, who said her daughter has autism and lacks the ability to speak or express herself.
"I have children," Jones cried. "And the fact that she can't talk, and the fact that she's probably hurting -- and Lord knows what this lady has done in the past -- it just breaks my heart."
The woman in the video has been identified as 54-year-old Yolanda Keith.
The director of the Child Resource Center in Palmdale said the sitter paid Keith to provide child care services to the girl in the video. The director said the child's mother picked Kieth from a list of names that was referred to her.
Detectives are investigating the incident in conjunction with investigators with the California Department of Community Care and Licensing, and the Department of Children and Family Services.
"It breaks my heart that she can't tell us what she's been through, but God knows that justice will be served," Jones said.
SEE ALSO: Toddler who wouldn't nap tossed by day care worker, caught on video