All members of the group - seven children and five adults - "were in the ditch, not on the pavement or gravel shoulder at the time of the crash" and were "wearing green highly visible safety vests", police said.
Officials said she had been removed from the home of her biologial parents and was placed in a foster home.
Treu faces four counts of homicide by intoxicated use of a vehicle.
He was fatally injured at a licensed daycare center in Wheaton, Wisconsin on October 30, with the 10 year-old girl now charged with his murder.
The unnamed child has been charged with first-degree homicide after the six-month-old tot died at a daycare nursery in Wisconsin, US.
Bond has been set for the man accused of a fatal hit-and-run crash in Lake Hallie.
Chippewa County District Attorney Wade Newell said after hitting the group, Treu then drove home to hide his truck in a garage before going to a party with friends, according to WQOW.
Treu and his passenger, who also turned himself in, allegedly told police that right before the crash they "had been intentionally inhaling chemical vapors," also known as "huffing".More news: AMC network announces the expansion of The Walking Dead universe
Nine-year-old Jayna Kelley and 10-year-old Autum Helgeson, both of Lake Hallie, were also killed.
As a western Wisconsin community grieves the deaths of three Girl Scouts and a parent who were struck by a pickup truck, authorities still haven't released the names of the victims or a fourth girl who survived.
In front of Halmstad Elementary, teddy bears, balloons, candles and a bouquet of flowers sat on two wooden benches Sunday afternoon.
"Our hearts are broken for the girls and families of the Girl Scouts of the Northwestern Great Lakes", CEO Sylvia Acevedo said in a statement, according to the Associated Press.
District superintendent Heidi Eliopoulos issued a message to parents saying, "This is a hard time for our students, families and staff".
"We will be providing ongoing support for both students [and] families and staff for as long as needed", Ms Eliopoulos said.