。
She talked back to him.
Literal
She [topic-は] him [to-に] talked-back.
言い返す is a 複合動詞 from 言う ('say') + 返す ('return, send back') — 'send words back' = 'retort, talk back.' Compared to 口答えする (more confrontational, often used about children or subordinates), 言い返す is more neutral — applies to any back-and-forth retort, in arguments or discussions.