Jane is a nightmare spirit called a Marra. 
The Marras are evil humanoid creatures that reside in the Huldrawood. They haunt the streets and houses of Trolberg at night, looking for timid people (often children) to scare and give them nightmares, often based on fears and insecurities of their victims. Jane herself seems to be the ring leader of the local Marra. She has lots of light blonde hair that she puts up in large pig tails, she has black eyes that glow green on command.