Six Flags spokeswoman Sharon Parker said the Texas Giant ride was closed pending an investigation into the accident, the Fort Worth Star-Telegram reported.
The victim's name had not been released.
"Our thoughts and prayers are with the family and friends during this difficult time," Parker said.
The woman is the second person to die at the amusement park. A 28-year-old Arkansas woman was killed and 10 other people were injured when a boat overturned on the Roaring Rapids ride in 1999.
The 14-story-high Texas Giant first opened in 1990 and re-opened in 2011 after a multimillion-dollar rovation, the newspaper said. It features a 79-degree first drop, which the newspaper said is the steepest in the world for wooden roller coasters, a 95-degree bank turn and riders reach a speed of 65 miles per hour.