What, cos all cunty-type women are delicate little flowers with tiny hands? And if we're not, we must really be men?
And anyway, if Rita Skeeter were actually a male trans person, then surely, being a non-Muggle, she'd have magically altered her jawline and hand size? We know that sort of thing's possible, Madame Pomfrey did it to Hermione's teeth.
(I can't believe I'm actually giving this brainspace. What does a "heavy jaw" look like anyway? I'm rubbish at face descriptions, never really did get this one, and google isn't helping.)