Who is Shar the Night Wisp from Wizard's First Rule and what is their importance?

Shar, the night wisp, is a tiny fairy-like creature who has guided Kahlan across the boundary between The Midlands and Westland. The trip has diminished her strength to the point that Shar cannot survive the trip back, and dies soon after the crossing. Before she dies, she tells Richard that all he has to do is utter her name, and the night wisps will help him.