。
She saved money for a rainy day.
Literal
She [topic-は] in-case [to-に] in-preparation saved.
万一に備えて貯金した — 万一 (まんいち, 'just in case') sets a low-probability hypothetical. に備えて ('in preparation for') uses the te-form of 備える. 貯金する (ちょきんする, 'to save money') is a standard financial suru-verb.