Janet was facing charges in connection to a bombing of a South American official outside the UN building, and was brought to Wentworth Detention Centre while awaiting extradition to the U.S.
Janet planned to escape with the aid of terrorists who would break in and free her, and struck up a friendship with Ros Coulson in the process, offering to take her along in return for Ros' help.
When Janet is first brought to Wentworth, she is sent straight to solitary so she doesn't interact with the other prisoners, however Ros happens to be in the next solitary cell and the two get talking.
Janet plans for Ros to drug the hot water urn in the staff room, with the hope that the officers will pass out after making themselves a tea or coffee. This is largely successful, except for Erica Davidson needing to phone the prison after hours - when she hears no answer, she goes to the prison with the police to investigate.
Janet clearly has no problem with the terrorists planning to kill officers and prisoners that get in their way (which thankfully doesn't happen), yet when things don't go as planned, Janet attempts escape on her own and is shot and wounded in the process.
She is taken away from Wentworth on a stretcher accompanied by Federal Police.