Darkness (Book Two, Buffy the Vampire Slayer)
Zoey Francis is one of the Scoobies. She was involved with Ethan Rayne's spell on Halloween, when she had been dressed as an assassin, which turned her into an assassin for that night. Like Xander remembers what he had turned into on Halloween, the military man, Zoey remembers. She knows how to fight, but she's learning how to do it again. She and Buffy can take on the things that go bump in the night together...
And might find someone to love along the way.