This npc follows you after you use the Whistle, an will grant quest in only certain areas. She will also fight for you, and does not cancel any quest if she dies.
While active this npc grants & completes quests, but only in certain locations, in order to get the quest you must either already have this npc summoned & following, or summon the npc at the given location for the quest.
You get this npc from the quest:
A Missing Intruder
|Noriel (Your Ally)|