A suburban Chicago girl has admitted to a Lake County judge that she stabbed to death her 11-year-old half-sister.

The 15-year-old Mundelein girl, unidentified because of her age, wept as she made the admission Tuesday. In a plea agreement, the girl was sentenced by Judge Valerie Ceckowski to juvenile prison until her 21st birthday. She will be eligible for parole in five years.

Lake County State's Attorney Mike Nerheim dropped two of three first-degree murder counts against the girl for the plea agreement.

Prosecutors allege the teen stabbed her sibling more than 30 times on Jan. 21, 2014. They say she later told investigators the younger girl didn't appreciate all she'd done for her.

The Associated Press is not naming the victim in this case because doing so would identify the defendant.