Shadow of the Sphinx

Shadow of the Sphinx is the 16th novel in the Charmed novels and is written by Carla Jablonski.

Summary From the Back of the Novel
Paige Matthews is having a minor identity crisis. She is slowly but surely embracing her long lost sisters' witchy ways, but she doesn't want to overstep her boundaries. After all, she wouldn't ever want to replace Prue Halliwell -- even if she could. So Paige considers it a stroke of luck when, one day, her experiments with magic turn her into a cat. Who knew she had a knack for shape-shifting?

One problem: She can't shift herself back. Her sisters inadvertently betray her when they deposit her at a local animal shelter. Suddenly she finds herself the familiar of a cult that worships ancient Egyptian deities, and is catapulted into ancient Egypt! Piper and Phoebe discover the identity of the stray cat and rally a rescue mission, only to discover another cat-woman, also entrapped within a fortress-like sphinx. This kitty is one feline femme fatale, and the sisters are going to have to put human heads together to defeat her!