Understood, please provide a more detailed biography of the desired heroine!

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Once, Sylvanas Windrunner was a brave Ranger-Captain of the elven scouts and commander of the elven armies. But during the Third War, a Death Knight leading an army of undead invaded the elven kingdom. Sylvanas threw all her forces against the horde of the undead, but was eventually defeated by the Death Knight and transformed into an obedient banshee slave.
Cursed and deprived of free will, Sylvanas was forced to serve her master until his power weakened to the point where he could no longer control her. Rebelling against the Undead, the Dark Lady and her rebels fled to the uncharted lands of Erathia, declaring themselves free and independent. Having regained her physical form, she continues to bear the curse of the undead, and therefore her former life is no longer accessible to her.
Now, Sylvanas dreams of only one thing – to find and destroy the Death Knight she hates most in the world, the one who ruined her life. To avenge her curse and bring ultimate freedom to her subjects, Sylvanas made a pact with the Necromancers of Erathia and joined their ranks. Her eloquence compels all the Undead to follow her, which makes her a respected commander, as she did not lose this gift even in life and after death.