Secrets (Sweet Valley High #2) by Francine Pascal

What Jessica wants, Jessica gets...even if someone gets hurt! 

Beautiful and ruthless, Jessica Wakefield is determined to be chosen queen of the fall dance at Sweet Valley High.  If she can win the contest, she's sure to win Bruce Patman, the most sought after boy in school.

The only person standing in Jessica's way is Enid Rollins.  When Jessica discovers the truth about Enid's past, she knows the crown is within her grasp.  She doesn't care that Enid is her twin sister Elizabeth's best friend--or that revealing the secret may cost Enid both her reputation and the boy she loves.