Serilda joins you on your quest to kill the dragon, as well as the unknown henchman of Alrik who controls it.
At some point in the game, Serlida comes to grips with the truth: If she allows herself to get killed, no more innocents will be harmed. She decides to sacrifice herself.
This too gives her Rooting Interest; it makes us identify with her.
In The Lord of the Rings, each member of the Fellowship is willing to sacrifice himself to prevent Sauron from returning to power.
This particular technique was also used extensively in the first Star Trek series, and in many of the succeeding Star Trek series as well. Kirk, Spock, and Bones never think twice about sacrificing themselves to save their comrades, and often risk their own lives to protect others.