Unlike 99.9% of manga characters (who aren't background or joke characters), she actually has some weight to lose, and you can actually tell by how she's drawn. But whether she
should is another question.
"Then you shouldn't have come to drink."
Cutting drinks is a significant amount of unhealthy calories you get rid of.
"You can just drink soft drinks."
And most of those contain a lot of sugar.
Switching to water, milk, or some other actually healthy alternative is a great way to do a lot difference with few means.
"Do you really need to lose weight?"
A question everyone should ask themselves if they want to try. And the answer is generally: Live more healthily. Weight is as bad as BMI for determining health. How long you can run is a much better metric.
I genuinely think she should see a therapist, those mood swings can't be healthy
It's a manga. Therapists don't exist. Not that I disagree.
One man's "She belongs in a therapist's office" is another man's "She's all I've ever wanted".
What other people want isn't necessarily related to what's healthy for them.