That's Annie, from the excellent BTAS episode "Growing Pains".
DCAU Clayface had the power to turn himself into several smaller forms so he could essentially be his own gang.
Annie was a "scout" self that a weak and injured Clayface created to go out and see if things were okay for him to come out into the open. But because he was weak she developed sentience in her own right as she got further away from him, and essentially became an amnesiac human girl, who Tim Drake's Robin developed feelings for after he encountered her. In one of the most disturbing scenes in the entire DCAU canon, Clayface reabsorbed her against her will so he could restore himself to health, essentially killing her.
Design-wise, she's based on Natalie Portman's character Mathilde in the movie "Leon"