Head games, by Mariah Fredericks.
In the Game, you can call the plays, make the rules—remake yourself, even. Judith is clever, stealthy and resourceful, playing a thief in an online quest controlled by—whom? But beyond this, Judith has her own reasons for wanting to hide, for wanting to protect herself from danger on the city streets and the cruelty of friends who have moved on to others and left her behind. However, a challenger from her online game has emerged as a real person and joined her on the sidewalks, proposing a whole new set of rules.