Margaret has always felt like her body isn't right. She isn't sure what it should be, but it shouldn't be what it is. The texture of her skin and the shape of her limbs and the entire concept of fingernails are just Not Good.
When she starts feeling insistently hungry and thirsty, even right after a meal and a glass of water, it's just one more indignity of having a body. Her parents are worried; food is expensive, but more importantly they worry it might be a sign of something wrong with her health. They tell themselves she's just having a growth spurt, and let her have seconds and thirds and fourths as long as plenty of it is vegetables. Margaret doesn't mind about the vegetables; at this level of hunger everything tastes amazing.