。
She refuted his argument.
Literal
She [topic-は] his [genitive-の] argument [against-に] refuted.
反駁する (はんばくする, 'to refute, rebut, counter') is formal/argumentative vocabulary — common in academic, journalistic, or legal discourse. Built from 反 ('against') + 駁 ('refute, contradict'). 議論 ('argument, debate, discussion') is the matter being refuted; the に marks what's being countered.