Final answer:
Laura Secord was the heroine who warned Lieutenant James FitzGibbon of a planned American attack in 1813 during the War of 1812.
Step-by-step explanation:
The heroine who warned Lieutenant James FitzGibbon of a planned American attack in 1813 was Laura Secord. During the War of 1812, Laura Secord overheard American soldiers discussing their plan to attack Lieutenant FitzGibbon's British outpost. She walked 20 miles through rough terrain to warn him, allowing the British to successfully prepare for the American attack and leading to their defeat.