She was born with an urge to wander and like other Windborn was given leave to explore the world beyond the forest for no more than a hundred years. 
After little more than a year, she heard word of the invasion of the north by Asavar Kul and that a human leader named Magnus was raising any army against him. It seemed like a great adventure and she crossed the Empire, finding the Imperial army camp she slipped inside and found the tent of the leader, offering her services as a Scout. Magnus accepted and she scouted for the army as they made their way north, confronting the horde in an epic and terrible battle at the gates of Kislev. 
Elessa kept close to Magnus in the battle, taking part in the decisive charge that won the battle and slew Kul.