Blood Sisters — Deborah Sherwood

They called themselves the "Loreleis." Six bright, attractive high school girls who had formed an exclusive sorority. Their secret initiation kept anyone else from joining their hallowed ranks. Until Kathi Harcort, the new girl in town, proved more stubborn than they had bargained for. But on the verge of becoming the seventh Lorelei, Kathi failed the final, fatal test....

Thirty years have passed since the Loreleis were disbanded. Thirty years since Kathi's mysterious and shocking death. Now the Loreleis are together once more on the eve of a class reunion. Only instead of six, there are seven of them. For Kathi has returned. And she's about to initiate the Loreleis into the hellish ranks of the BLOOD SISTERS