The 23-year-old American maintains she was just trying to defend herself and never meant to offend or slander anybody, her lawyers said.
Knox had claimed she was beaten and put under pressure by police during questioning over the slaying of Meredith Kercher three years ago. She said police repeatedly called her a "stupid liar."
Police denied misconduct and filed charges saying Knox's comments were slanderous.
Judge Claudia Matteini issued the indictment ruling after a hearing behind closed-doors in Perugia at which Knox spoke. The judge scheduled the trial to begin on May 17.
Knox is serving a 26-year prison term after she was convicted of murder and sexual assault in December. She has denied murdering Kercher, a 21-year-old Briton, and her appeal is set to begin Nov. 24.
Curt Knox, Amanda Knox's father, told The Early Show on CBS on Monday that "this is going to be her chance once again to have that wrongful conviction overturned."
Lawyer Carlo Dalla Vedova described Knox as "very sad and worried" but also ready to face the appeals trial.
Knox's ex-boyfriend and co-defendant at her murder trial, Italian Raffaele Sollecito, was convicted and sentenced to 25 years. A third person, Ivorian Rudy Hermann Guede, was convicted of murder in separate proceedings and sentenced to 30 years in prison, which was cut to 16 years on appeal.
All have maintained their innocence.