Shark Princess: Shark Party! (Shark Princess #2) by Nidhi Chanani
From Viking Books for Young Readers:
Kitana and Mack are back!
Mack and all the other sharks are going to a party, but Kitana doesn’t feel like shell-ebrating. Then she learns a mysterious shark in the deep ocean hasn’t been invited. With Mack’s sparkly sharkle lighting the way, the shark princesses set off on their newest adventure into the deep sea!