The Witch's Heart by Genevieve Gornichec

Angrboda's story begins where most witches' tales end: with a burning.  A punishment from Odin for refusing to provide him with knowledge of the future.  The fire leave Angrboday injured and powerless, and she flees to the farthest reaches of a remote forest.  Ther she is found by a man who reveals himself to be Loki, and her initial distrust of him transforms into a deep and abiding love.