The woman is believed to have been on the verge of being radicalized and taken abroad to a terrorist group by a man with whom she had begun a relationship.
The man is already known to Säpo and is considered to be radicalized and violent.
The investigation reveals that the 18-year-old "began a radicalization process towards violent extremism" and that "there was a rapid escalation," according to Säpo.
The woman denies the allegations.
