A teenage boy also admitted to a similar juvenile charge and was ordered to serve five years on probation.
Authorities say two girls and two boys plotted to shoot specific administrators and students at Cascade Junior High School and Cascade High School in April.
Marion County Deputy District Attorney Kurt Miller says the hearings took the place of a trial for the two teens.
The girl is awaiting disposition, the equivalent of sentencing in adult court, on Nov. 4.
Information from: Statesman Journal, http://www.statesmanjournal.com