According to
this, if she really is 156 cm and 48 kg, her BMI is 19.7, which is actually normal weight.
Yeah, who cares about her weight? And yeah she seems to be somewhat of a heavy eater (not piggy, but just likes sweets; face it: who doesn't?), but she probably just has a fast metabolism.
Have you guys noticed how active she is? Thank God she's not anorexic.
Apprentice is right: Japanese people generally are small and thin.