Who is Lizzie from The City of Ember and what is their importance?

Lizzie is Lina's classmate. Shee is assigned to the supply depot, where she befriends a boy who has access to the hidden supplies. When Lizzie benefits from the friendship (receives goods), she tells Lina she isn't doing anything wrong..... that there aren't enough cans of food for the residents of Ember, and that it would create problems if everyone knew of the extra food and supplies.