Makayla McEvoy was at Wyangala Dam in Wyangla Waters State Park with her family New Year's Day when the animal attacked, causing injuries to her face, arms, back and legs that required hospitalization, the Western Advocate reported.
Makayla's mother said she "just froze with fear" at the sight of her daughter being attacked.
"As I turned around I just saw it and it didn't register straight away what happened," Emma McGovern said.
Stepfather Mitch McGovern and other holidaymakers came to the rescue.
"I ran down. It was on top of Makayla and I just kicked the kangaroo," McGovern said.
Makayla was taken to a local hospital where she was treated and released.
Wildlife Information, Rescue and Education Service large mammals coordinator Kimberley Parker said it was very out of character for a kangaroo to attack a person.
"I'm just gobsmacked ... they should have jumped away, they're more scared of us," she said.