Witchlight — L.J. Smith

Keller is a black panther. At least when she's not being a tough, no-nonsense seventeen-year-old girl. She's a shapeshifter who grew up on the streets and will do whatever it takes to survive. But when Circle Daybreak hires her to protect a new Wild Power, Keller meets her match.

Iliana Harman is a blond ditz who's been raised as a human, and whose only concerns are clothes, boys, and parties. Can this clueless bit of fluff really be the legendary Witch Child, one of the four teenagers who can fend off the end of the world? Can Keller persuade her to stop shopping long enough to take her destiny seriously? And what about Galen, the gorgeous boy destined to be the Witch Child's soulmate? He and Keller are falling in love, but it's a love that will destroy everything. Keller knows she has to give him up -- but her heart won't listen.

Meanwhile, the Night World is closing in, to kill all three of them...