Callie was a best friend to Katie Brown since they were babies until she dumped her to join the Popular Girls Club. She can sometimes be nice and other times not. She declares a war on Katie in Katie and the Cupcake War and became a rival of the Cupcake Club. A new girl named Olivia decides to take over the club and renames it the BFC (Best Friends club). After the BFC was formed, Callie and Katie then had peace together. After the Cupcake War, there is no more rivalry in the rest of the books. She and Katie were no longer best friends, but are at least friends.
Callie is tall with curly blonde hair and blue eyes. She and Mia get glasses in Mia a Matter of Taste. Callie is very nice to Mia (in Mia in the Mix), and she is nice to Katie sometimes. She can be charming when she wants too, though. Callie has a crush on Matt Taylor, Emma Taylor's older brother. She is close friends with Olivia Allen, Bella Kovacs, and Maggie Rodriguez, the other girls in the BFC. She also used to be friends with Sydney Whitman, the former leader of the PGC (the old group name) who moved away.