Don't be obtuse. What color was her hair? How tall was she? What was she wearing? None of that detail is present. This isn't scene-setting. It's a subtextual comment, and it's a clumsy and ignorant one. That's what bothered me about it: it's just bad writing. We get it, we get it: the author thinks lower-middle class families raise fat kids on junk food. Aha! There's one now!