@Hacete, it seems you misread what the mother said. The mother said she shouldn't NOT eat, and trying to make sure she doesn't try to starve herself to lose weight. The mother then suggests that, rather than not eating, it would be better to do more exercise to lose weight, while still getting enough nourishment.
@throwaway4ccount Now, I get it. But those word arrangement though, shouldn't it be like "You shouldn't stop eating" or "You can't skip meal" something like this.