。
She did the work effortlessly.
Literal
She [topic-は] effortlessly that work [object-を] did.
楽々と is a reduplicated adverb derived from 楽 ('comfort / ease') — the と here is the と that fixes mimetics and reduplicated adverbs to manner-adverb position. The reduplication intensifies the sense of ease, painting the action as effortless and unhurried. やる is the slightly more casual / colloquial counterpart to する ('do'), with a hint of 'getting things done' or 'pulling off' rather than just doing. 楽々と やる carries an implicit admiration — the speaker is impressed by the ease.