Lizzie Manning is a student Neptune High. Veronica describes her as the 'oversexed, overlooked younger sister' of Meg. Her parents always seem to compare her to Meg and because of that, she resents her sister.
Though she doesn't always like her sister, she does indeed love her, which is shown when she humiliates Meg's ex boyfriend for talking dirty about her. She comes to Duncan for help when the teachers are going to clean out Meg's locker. She brings Meg's secret laptop with files that would make her parents pull the plug out of Meg's life support. Veronica calls in Mac to decrypt the laptop and they take the files.