Definitely some exposure challenges with this image. Some fill light image right would definitely have helped to preserve detail in her hair and top. Her expression and pose rather make me think that you snuck up behind her and shouted "Smile" when she didn't want to have her picture taken.
Try framing/cropping your subject in a flattering way. The area of her body is 3-4 times that of her head in your image. Your goal as a photographer is to draw attention away from her weight, and draw attention to her pretty face.