|Weiss, you dumbass!|
SPOILER ALERT - Plot details for NIER follow.
Most of this information comes from additional cutscenes during and after the boss battle as 9S in the second playthrough. Simone's appearance comes from her desire to be beautiful in order to gain the affection of another machine lifeform (presumed to be Jean-Paul). Through a series of silhouetted cutscenes shown after each hacking session performed by 9S, we learn that Simone began as a standard biped machine, but sought to modify her body in an attempt to become beautiful. This included full body modifications and eating androids, which ultimately lead to her losing her sense of self.