You could always revert to a previous save game perhaps Lord, if you wanted to keep fair Kerrielle alive and still have the little amulet quest. Doing just that one extra sub quest adds that bit more depth to the game.
I've also been meaning to go back to her and purchase back the amulet now that I'm less financially challenged...
I never actually used the potion she gives for Xydusa, as the ethical dilemma which faced my party of the uncertain longevity of the potion versus an instant potent XP bonus from killing her immediately, made me lean heavily towards the latter. I never realised at the time I was so near a bonus trait until much later!
Resting in opulence under Oakenmir,
Cerebrodragon