Crews were dispatched at 6:17 p.m. to the school at 152 N. Vermont Ave., Margaret Stewart of the Los Angeles Fire Department said.
Urban Search & Rescue personnel placed a "capture strap" around the woman and then raised her to the roof, working slowly to prevent injury, Stewart said.
The female's predicament was "related to an earlier jumper incident,'' Stewart said.
An LAFD battalion chief told a videographer at the scene that the woman was trapped for about two hours before she was found and it took about 90 minutes to get her out.
Police were notified of a possible jumper atop the school but were unable to locate anyone after a search involving a helicopter. A school police officer who went up to the roof heard the woman calling for help, the chief said.
The woman was trapped in a 2-square-foot space, he said.
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