Mia has a crush on Josh Richter, the boyfriend of popular cheerleader Lana Weinberger, who often makes fun of her, though she also unknowingly harbours feelings for Michael, the brother of her best friend Lilly Moscovitz.

Mia's father, Philippe Renaldo, who has recently recovered from testicular cancer, pays a visit.

Mia refuses to move to Genovia so she and her father form a compromise; she will remain in New York with her mother during term-time but spend her holidays in Genovia and attend daily princess lessons with her formidable grandmother, the Dowager Princess Clarisse Renaldo.

Mia grows disillusioned with Josh during their date and realises he is only using her for the publicity after he deliberately kisses her in front of the paparazzi.

Mia loves to write, has a tendency to obsess over everything that happens to her, is a vegetarian, identifies as a feminist and is currently failing algebra and many other subjects.

Lana Weinberger: Head cheerleader, initially Josh's girlfriend, dislikes Mia and puts her down throughout the book.

She originally is shunned because her overprotective father forces her to have a bodyguard (Wahim), but she and Mia quickly become close.

In response to both writers, Hanna Liljeqvist has observed the overall ambiguity of the fictional diary as medium, which reinforces traditional methods of women's storytelling.

She has similar qualities, but her father dies two months prior to when the movie begins, and her last name is Renaldi instead of Renaldo.