What is the best method to kill Elvarg the Dragon for the Dragon Slayer Quest in Runescape?

Elvarg is a slightly stronger version of a green dragon. She is the dragon that players have to kill in Dragon Slayer quest in the dungeon under Crandor. She is also the only dragon available to non-members that can be attacked. However, players may only enter her lair whilst doing Dragon Slayer. You cannot attack her once you have completed the quest.