Melayna and the Rise of the Shadow Master

In the fourth book we are taken to the dark side where we find Melayna, a girl given over to a dark lord by her parents to be his slave/servent. years later she is a favorite of the dark lord and is sent on a mission to find and destroy the chosen one, the boy that is destined to kill the dark lord, but upon meeting this boy, melayna realizes that there is a different life than the one she was brought up in and decides to help "The White Rose" instead of destroying it.