A Methuen teen was killed last night and her passenger seriously injured when the 2004 Lincoln LS she was driving northbound on Route 495 in Haverhill rolled over and crashed, state police said.Police said an off-duty Methuen firefighter, two off-duty troopers and Haverhill firefighters pitched in to free the driver and her 19-year-old passenger from the wreck and render first aid.The crash occurred about 6 p.m. yesterday.