Brágha Fellwinder must be defeated before she can pass on her fell knowledge.
Brágha Fellwinder has gone to the tower of Caivád Sâr, in central Elderslade.
You should defeat Brágha Fellwinder before she can pass on the knowledge of the crystals and the corruption her spells bring.
Borghild is in the Angmarim tower of Caivád Sâr in central Elderslade.
Talk to Borghild.