Prosecutors presented the preliminary charges against her and a 24-year-old man suspected of being her accomplice in a court hearing Tuesday in Holbaek, northwest of the Danish capital.
Prosecutor Kristian Kirk told The Associated Press after the hearing that the suspects obtained chemicals and tried to produce explosives with the intent to commit terror attacks against the two schools.
He said police thwarted their plans by arresting them. He declined to give other details.
The suspects, who were not identified, deny the charges. The court extended their pre-trial detention until March 30.
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