Fifteenth century, France
Heroine to Roman Catholic France at age 17 (1429 CE), after she rallies French troops to lift the British siege of Orleans.
Two years later in the Hundred Years War, at age 19, she is captured in Rouen, France and burnt at the stake by her British captors. She thus enters immortality.
Her burning at the stake will not advance British fortunes, to put it mildly. Joan of Arc is later canonized, in 1920.