Lizzie is one of the kids living in East River Ruby encounters on The Darkest Minds .
Before the events of The Darkest Minds , Lizzie had been hiding out at East River for close to two years, after having escaped the PSFs who had pulled over her parents car in Maryland. Eventually, she met up with a tribe of Greens and foundher way to East River.
The Darkest Minds
They first meet Lizzie when they arrive to East River with the kids on patrol who found them. She sees the fruit they are bringing from their last "hit", and is visibly excited since, in her own words "[They] hadn't had fruit in ages."
She works in Storage; doing things like sorting the food, which is where Ruby is initially assigned to, before Clancy offers to teach her how to better use her abilities.
In the climax of the book, Clancy gets into Lizzie's minds and makes her cut herself and go after Ruby, to tell her Clancy is in danger. Ruby doesn't fall for the act (later realizing that the blood is, in fact, not Clancy's) but follows her regardless, and ultimately frees her from his control.
Ruby describes her as being around fourteen or fifteen and having numerous piercings in the cartilage of both ears, as well as cropped blond hair.