“It is too ‘eavy, all zis ‘Ogwarts food,” they heard her saying grumpily as they left the Great Hall behind her one evening. “I will not fit into my dress robes!”
“Oooh there’s a tragedy,” Hermione snapped as Fleur went out into the entrance hall. “She really thinks a lot of herself, that one, doesn’t she? (Harry Potter 4 [US Version]: p.404)[Bold font is mine]
N.B.: Fleur is one of guest students from a foreign school. She is very proud. Hermione is one of the students in Hogwarts, the host school.
I’m not sure if ‘that one’ in this sentence means ‘that girl’ (a noun phrase) or ‘considering what she said’(an adverbial phrase). I’d like to know the meaning of that one and its function.