The book opens with a girl raised by an old man (can't remember if he's human) and she lives with a horse. Along the course of the story, she finds out that she was actually born a few hundred years before, her dad was an elf(?) necromancer, her dad gave up necromancy to be with her mom, another necromancer raised an army of the dead and framed her father for it, the army killed the second necromancer's sons, and the girl and her guardian rode a unicorn in some sort of time jump. The unicorn lost it's horn though. The necromancer waited until he caught up to her time to try somehting (I think he was trying to restore his sons). The girl eventually has to choose who will be saved by the single teardrop the dying unicorn produces. She uses it to restore the unicorn, and in the process the unicorn regains it's horn. It then heals everyone else. As you can see, I think I remember this plot pretty clearly, but I read the book probably 10 years ago and can't recall the name of it. Does anyone remember the name or author? Thanks