However, the magistrate suspended the sentences and warned the teenager about her future conduct.
The 15-year-old was among a group of students held by members of the Island Special Constabulary Force (ISCF) in downtown Kingston last November.
She was found with a knife and an ice pick in her bag and claimed she was carrying the weapons because she was worried about a rumoured spate of abductions.
However, the ISCF members said she was part of a group of children who repeatedly skipped school and idled downtown.
It was noted that other students were found with clothes in their school bags and tried to evade the police before they were held.