What is Sister Margret doing in Chapter 20 and what happens with her?

Sister Margret, is following the Sisters of the Dark. The Sisters of the Dark know that Sister Margret is following and a young wizard, Jedidiah, helps them to murder her. Sister Margret sends the knowledge of who killed her into a necklace she is wearing, a necklace that Jedidiah made her, before she dies hoping that someone will find it.