Narmeleth told you the tragic tale of her fall and her transformation into Amarthiel, the Champion of Angmar.
'${PLAYER}, I wish to do some good in the fight against that evil which I created. Mordirith has recovered Narchuil, and doubtless he will seek to use its powers soon.
'Mordrambor is arrogant, but he has skill in the Dark Arts of the Enemy and is no less wicked than his master. He, too, remains a threat that I allowed to persist.
'I wish to aid in healing the hurts I have inflicted upon the world, even if by the least act. If you would but speak to Lord Glorfindel for me, I will accept my judgement, whatever it may be.'
You will automatically travel to Rivendell in the Trollshaws when you accept this quest.
Glorfindel is in Rivendell, south-east of the House of Elrond.
Narmeleth has asked you to speak with Glorfindel on her behalf.
Glorfindel is in Rivendell by the Falls of Imladris, south-east of the House of Elrond.
You should return and speak with Glorfindel in Rivendell.