She was last seen Wednesday night.
Authorities believe she may be with her biological mother, Megan Boynton, twenty-five, who does not have custody.
Police have not been able to reach her, about the incident.
No description of either of them, beyond a photo, was released by authorities.
When last seen, Kassidy was wearing a multi colored fleece jacket, a yellow bumblebee shirt, and black pajama pants, but not shoes.
Anyone with information should call the South Jordan Police Department at 801-840-4000.
They were found in Las Vegas, Nevada, on Friday afternoon.