Elisabeth was instead married to Frederick IV, Duke of Lorraine. The contract was signed on 6 August 1306 and they married in 1307. From this marriage Elisabeth became Duchess of Lorraine and Frederick was able to support Elisabeth's brother Frederick the Fair, to become Holy Roman Emperor. Elisabeth's husband was captured at the Battle of Mühldorf, where he was fighting for Elisabeth's brother and was released by the King of France. Elisabeth became known as Isabelle in Lorraine.