Long story short - she was a mercenary(or head hunter as you want to call it), then she traveled with some kinda-random knight, Clancy Slate and fall in love with him. They were adorable and brutal at the same time, going around Azeroth and Outland on the adventure called "looking for troubles" for some time. And sadly...one day they found their troubles. Clancy was slain in some random battle, leaving Siel alone in their little house, on the edge of forever green plains of Nagrand :C