Answer:
The prophecy that Lyra would be a betrayer came true in the sense that she inadvertently played a role in the death of her best friend Roger. As part of Mrs. Coulter's plan, Lyra was lured to Bolvangar and convinced to help rescue the other children who were being held captive there. In doing so, she unknowingly led Roger to his death, as he was used as a sacrifice for Mrs. Coulter's experiment.
Despite this tragic outcome, it's important to note that Lyra's actions were motivated by her desire to do what was right and save her friend. She was not aware of the full extent of Mrs. Coulter's plan, and once she learned the truth, she was determined to stop her. Lyra's courage and determination were key factors in ultimately thwarting Mrs. Coulter's plans and saving the other children from Bolvangar. In the end, Lyra's true nature as a hero and a savior outweighed any perception of her as a betrayer.