I agree with the assessment that the changes to the Nightsong/Aylin also heavily impacted Halsin. Aylin in no way fits anything that would reasonably be called the Nightsong and whatever it was originally supposed to be probably made a lot more sense. Having to shift Aylin and therefor Isobel and Shadowheart around so much after changing the Nightsong definitely hit Halsin's involvement with the Shadow Curse pretty hard.
