The guilty verdict was passed at Holbæk Court on Tuesday morning, reports newspaper Politiken.
The 17-year-old will now face sentencing for planning to commit acts of terrorism in Denmark.
Over 50 people were present in the courtroom as the verdict was read, including the girl's mother, reports the newspaper. The girl is said to have remained emotionless during the proceeding.
“The entire jury and all judges have reached the same result,” presiding judge Peder Johs Christensen said.
The girl, who was 15 years old at the time of her arrest in January 2016 and has been remanded in custody for 16 months, planned to used explosives to attack two schools, concluded the court.
The 17-year-old, who was born and raised in Denmark, converted to Islam in 2015, some months before her initial arrest.
During the trial, at which she pleaded innocent, she was described as having undergone a drastic change in interests from boys and shopping to holy war in the space of just a few months.
She previously told the court that her interest in terror organisation Islamic State began because she found it “exciting.”
She is now considered a terrorist by the Danish legal system.
The girl will be sentenced for planning terror attacks against two schools – her own former school, Sydskolen in Fårevejle, western Zealand; and a Jewish school in Copenhagen.
Manuals on how to make bombs and prepare explosives were found when the girl was arrested at her home in the western Zealand village of Kundby – from where she takes the name given to her by media - last year.
During her 15-month stay in custody prior to trial, the girl also wrote a long part-biography, part-fiction text in which she allegedly explained the thoughts behind her actions and imagined herself as a fully-fledged jihadi planning the attacks. This text was later used as evidence by the prosecution.
Prosecutors also presented social media correspondence, letters and other documents in which they argued the girl expresses herself as someone who has been “quickly radicalised”, reports Politiken.
Defence lawyer Stage argued that the girl had had no intention of carrying out the attacks, but wrote the things she did in an attempt to seem “exciting”.
According to the verdict statement, the attacks planned by the girl were not carried out because she had not received an order to proceed with the attack against Sydskolen and because she was arrested before she could carry out her plans against Carolineskolen.
Although police found chemicals that can be used to make explosives at her home, she had not succeeded in actually making bombs.
But the court ruled that there was “a punishable attempt at terrorism, since it was her intention to bring a bomb to two schools and detonate it.”
A verdict had been initially due in the case earlier this month, but was delayed after the prosecution applied to present new evidence, even though this stage of the trial had already been completed, in an unusual step.
This evidence consisted of letters in which she further underlined her intentions to carry out a terror attack, it was later reported.
Sentencing will take place after cases for it are put forward by senior prosecutor Kristian Kirk and the girl's defence lawyer Mette Grith Stage, reports Politiken.
The prosecution has requested the girl be imprisoned indefinitely, an option in Danish law if a person is found guilty of a very serious crime and judged to be a risk to society.
She will be sentenced tomorrow.