I think it's a combination of the sheer thickness of the arms warping the proportions, and the simple anatomy situation - when your arm and body take up so much space, your arms don't go as far - so while her arm/hand is reaching as directly as possible to put her hand in her pocket, because there's so much to get around, if I (BMI 20) put my hand in my pocket just like that, my arm would be bent at a maybe 100 degree angle and way out from my body to the side, making it look as long as it is.