Oh fuck off Japan, calling 52.6kg overweight for an adult woman. God I hope no one reads this as a serious weight-loss manga over there, they'll bloody kill themselves.
While I agree that it's probably be better to deal with a more average person, a weight in the lower 40s of kg isn't unusual for a serious, young, female, long distance runner. If they'd said she was a gymnast, if probably would have been more believable, but still not an average person for sure.
And yes, there is a disconnect between the kind of training that a long distance runner does to get there, and the kind of low calorie diet plus light exercise that this manga is using, but that doesn't mean that everything held within is bad advice.
The recipes themselves seem pretty normal for diet food.