。
She became famous overnight.
Literal
She [topic-は] at-one-bound famous became.
一躍 (いちやく) is a Sino-Japanese adverb meaning 'at one bound / in one leap' — the kanji 一 ('one') + 躍 ('leap, jump') paint a clean picture of sudden ascent. It's reserved for fame, success, or status changes: 一躍トップに躍り出る ('shoot up to the top in one leap'). The pattern ~になる takes a noun or na-adjective and means 'become X'; here 有名になる makes 'become famous' a single change-of-state predicate. The whole sentence has the rhythm of a news headline — compact, formal, punchy. It's the Japanese equivalent of 'shot to fame.'