Good Switch, Bad Switch is a novella written by David Cody and Bobbi J. G. Weiss. It was first published in 1997 and was the third book in the Sabrina the Teenage Witch book series.
Description[]
Achoo!
Sabrina's got spellfluenza, a nasty little witch virus. Every time she sneezes her powers pop out of her and into the next person. Another sneeze and they're back again -- whew! It's not bad at first -- Sabrina only sneezes in pairs. But then Libby Chessler gets in the way of a solitary achoo and...uh-oh.
It doesn't take Libby long to figure out she's picked up some powerful magic. Now there's just one thing she wants...more! After all, world domination isn't out of the question!
Sabrina's challenge is clear: Follow Libby on her search for bigger and better powers, and stop her.
But can she do it as a mere mortal?