Elena is a missionary and a healer NPC that can first be found in West Ardougne. She is rescued during the Plague City quest and then asks you to recover and identify the plague sample in the Biohazard quest.
Her Picture can be found in her parent's house in East Ardougne.
During the Biohazard quest the player helps her uncover the truth about the plague.
Before the player starts/finishes the Plague City quest she can be seen in the house east of her parent's house. However, when the player attempts to open the door they will find that it is locked.