This gay little scenario would backfire hideously. All it would do is send the pooner scampering to her social media to gush about the heckin' manly and ~affirming~ thing that just happened to her! The way to utterly destroy a pooner is to 1) also be a woman and 2) in your friendliest gal-pal voice hit her with a "cute top! I have one just like it but in green!" or, if you want to go nuclear: "Your pixie cut looks sooo gorgeous! Really accentuates how delicate your jawline is!"
If you see the scar, she's already lost.
Regarding Rowling's refusal to coddle fatties: I've never read Harry Potter but I've read the Strike books and it's pretty evident Joanne is turned off by porkers. Sometimes sympathetic characters are a little chubby, which is only mentioned in passing, but when villainous characters are fat it's described in much more lurid, disgusting detail (the seventh book in particular has a very memorable fat rapist). The protagonist is mildly overweight for most of the series which he obviously hates and feels ashamed of until he goes on a diet in the latest book (basically, Rowling's not going to let him fuck the Mary Sue self-insert without losing the extra pounds first). My hunch is that Rowling is "fatphobic" in the sense that she's grossed out by morbid obesity and who can blame her, that shit is almost as gross as troonery.