From the fifth book in the Fabulous Five series of young adult novels, The Bragging War (1989), by Betsy Haynes.
Laura McCall is bragging about everything her dad lets her do, and implies that she'll invite everyone over and they'll do something fun, but secret. In an attempt to one-up Laura, Beth decides she'll have a slumber party with boys and tells everyone about it, so everyone who was planning on going to Laura's party wants to go to Beth's instead. However, Beth can't have a party because she's grounded. Laura shows up at her house on the designated sleepover night and when she finds no one there, Beth and the rest of the Fabulous Five are made out to be fools. After Beth tells everyone that Jana is related to rock star Trevor Morgan, things really get out of hand, until his band comes to town and creative, resourceful Beth finangles a way to see him, and he devotes their entire concert to The Fabulous Five. The book ends by Jana asking Beth to swear not to make up any more outrageous stories to make them look stupid.