The PGC (Popular Girls Club) is a club containing Callie, Maggie, Bella, and their leader, Sydney. They are mean girls and are the rivals of the Cupcake Club. Sydney Whitman always teases and insults the Cupcake Club. In book number six: Mia's Baker Dozen, Sydney spread a rumor about Jackson Montana becoming bald. Luckily, she moved to California later on. Unfortunately, Olivia Allen appeared in book ten: Mia's Boiling Point. She was friends with Mia for a while, but their friendship broke apart when Mia realized that Olivia was using her and was a cheap plastic friend. Olivia ditched her for the PGC.

Callie Wilson was Katie's best friend before she joined the PGC club. The two girls were the best of friends, whose families were really close. Callie Wilson has blonde hair, and she is pretty tall.

Maggie Rodriguez is silly and fun. She's like Sydney: mean and insulting. But, she's mostly okay if Sydney isn't there to boss her around. In the Cupcake Diaries series, it was described that she had frizzy brown hair. In book five: Batter Up, Katie, she tried out for the softball team without Sydney's approval. After joining the club, Maggie made friends with Mia, so they started hanging out for a while. When Katie found at about this, she was really upset for she thought that her best friend was leaving her. Overall, Maggie is fun and silly.

Bella Kovacs is a mysterious goth girl. She dyed her hair black, and she puts on tons of white makeup. Her real name was Brenda, but she changed it to Bella, the vampire girl in the Twilight book series. She has been known to act weird around people, and everyone thinks its because she likes vampires.

Sydney Whitman is the leader of the PGC. She has long blonde hair, and she's into fashion, like Mia. In book three: Emma on Thin Icing, Sydney let Mia joined the club, but she refused. They were friends for a while, but it didn't work out. She later moved away from Maple Grove, which left the Cupcakers happier than they've ever been before. But after that, the mean and pretty Olivia took her place. She comes in Mia's boiling point and Mia tries to befriend her, but she realizes that Olivia is nothing but a fraud and a cheap friend.