。
She quickly got dressed.
Literal
She [topic-は] quickly clothes [object-を] put-on.
すばやく is the adverbial form of the i-adjective 素早い ('quick / nimble'). Unlike 早く (the adverb of 早い 'early/fast'), 素早い emphasizes nimbleness and reaction speed — the 素 (literally 'plain / unadorned') functions as an intensifier here, giving 'pure speed'. Useful for actions completed with quick motor coordination: すばやく動く ('move quickly'), すばやく振り返る ('turn around quickly').