In an Absent Dream by Seanan McGuire

 This fourth entry and prequel tells the story of Lundy, a very serious young girl who would rather study and dream than become a respectable housewife and live up to the expectations of the world around her. As well she should.

When she finds a doorway to a world founded on logic and reason, riddles and lies, she thinks she's found her paradise. Alas, everything costs at the goblin market, and when her time there is drawing to a close, she makes the kind of bargain that never plays out well.