Miss Popular Book 5 by Tamara Hart Heiner

Cassandra is excited to celebrate her 11th birthday with her new friends from Arkansas. But when her party falls on the same day as another, more popular girl, she realizes that the people she thought were her friends might not be. As she worries about who will be at her party, her cat suddenly gets sick, and having a birthday party becomes the least of her problems.

Readers of Junie B. Jones will love meeting Cassandra!