Why did the girl have to lose her memory?

Scientist of the heart: Narumi Saku's challenge

Following the events of The Sheriff and the Satellite Kid, Sheriff Hall and H-725 (using the official identity of Charlie Warren) still get no rest from the military - because the little alien has not yet grasped the meaning of keeping a low profile. They are constantly on the move, and H-725's father has had to pick them out of a tight spot too many times already.