As the show progresses, she undergoes various "image" changes, including becoming rebellious, disrespectful, and rude in the episode "Bad Girl McGuire". Lizzie constantly gets into arguments with her younger brother, Matt, but is well-aware of what is right and wrong.
Lizzie is a sweet, beautiful, honest teenage girl, who always knows when to do the right thing. She sticks up for her friends, but sometimes she needs reminding to as shown in some episodes. She is very kind and is even nice to her enemies, such as Kate Sanders. All Lizzie wants to do is get by life one step at a time. She is always trying to impress her crushes, such as Ethan Craft. She often has the urge to try to become part of the "popular crowd", as exemplified by her "arch enemy" (and former friend) Kate. Sometimes when she does something that gets her temporarily popular she decides that this sort of life is not for her and gives it up, as shown during the time she becomes a teen model and the time she dated a celebrity. Lizzie is allergic to strawberries and oyster sauce.
She once said that she hates Matt so much that she believed that she is allergic to him. As a running gag, Lizzie shows she seems to have a crush on her best friend Gordo. She even kissed him twice. Its seen at the end of the movie that they had become a couple.
Miranda Sanchez is her other best friend. Lizzie has known her for a long time and will do absolutely ANYTHING FOR HER.
Kate use to be Lizzie and Miranda's best friend until she became popular. They renewed the friendship in the movie.