Caroline Fu is one of Allie's friends at Pine Heights Elementary. She is the top speller in Mrs. Hunter's class, and, despite losing at an out-of-school competition, has a very large vocabularly and is very smart. She can read very fast, and read each of the Harry Potter books (even the long ones) in an day.
Caroline is kind, but not overly sweet and considerate like Erica. She is not as strong against peer pressure as Allie, but not as aware of it as Sophie, either. When Cheyenne made all of the girls in Room 209 "go with" boys, Caroline pretended to go with Lenny Hsu in the hopes it would make Sophie be her friend again, but thought the whole thing was stupid. She is quite a bit like Allie, as she is smart and tends to be independent. Out of Allie's four friends, Caroline is arguably the least developed, not having any storylines of her own.
In the first book, Caroline is not very prominent, however when Allie comes to visit Pine Heights Elementary she, Erica, and Sophie show her their secret place. Erica apparently told her and Sophie about Allie, and that she had a big imagination, so she could go there. Caroline, along with Erica and Sophie, show Allie their favourite game, Queens.
Book 3: Best Friends and Drama Queens
Caroline was on vacation over Christmas break, and, when seeing Erica at the baggage carousel in the airport, told her that she had big news, but was dragged away before she could say anymore. Allie was very excited about the big news, but it turned out only to be that there was a new girl moving into Mrs. Hunter's class, as supposed to being adopted and having movie star parents or having a horse. The new girl turned out to be Cheyenne, who soon Caroline, Allie, Erica, and Sophie started to dislike very much. After Cheyenne starting "going with" Patrick, she convinced Sophie to "go with" Peter, because she said otherwise she would tell Peter that Sophie liked him. Sophie blamed Caroline for this, because she told Cheyenne about Sophie liking Peter in the first place, and after asking Peter to "go with" her refused to speak to Caroline. To try to shock Sophie into talking to her, Caroline starts to "go with" Lenny (though she actually never did, she just pretended but never asked him), however it doesn't work. Soon, neither Caroline or Sophie will speak to each other. Eventually, Caroline's mother (along with almost every other mother of children in Room 209) calls Mrs. Hunter about the children "going with" one another, and Mrs. Hunter breaks up all the couples. Sophie and Caroline become friends again.
Book 4: Stage Fright
When Mrs. Hunter announces the play Room 209 will be performing for parent's week, Caroline, who is not that interested in acting, wants to be the unplug-when-not-in-use unicorn (who instructs Princess Penelope to unplug appliances when they are not in use to decrease fire risk), though she would rather work backstage. She is the only girl who tries out for the unicorn and gets the part. Later, when Sophie is taken off of the play for being rude to Allie, Caroline goes to Sophie's house with Allie and Erica to convince Sophie to come back to school and apologize to Allie so Cheyenne will not get to play the princess.
Book 5: Glitter Girls and the Great Fakeout
Caroline, along with Allie, Sophie, and Erica (and somewhat Rosemary), is super excited to go to the Little Miss Majorette Baton Twirling Twirltacular at the middle school to support Erica's sister, Missy. When Allie says that she can't go because she "has" to attend Brittany Hauser's party so her mom can keep her job, Caroline is disappointed but sympathetic to Allie. Caroline goes to the Twirltacular with Erica, Sophie, and Rosemary on Saturday, and presumably has a good time. When Allie realizes she has made a terrible mistake and comes home from the party, Caroline, Erica, Sophie, Rosemary, and Allie all go to the Twirltacular finals on Sunday.