。
She remained single her whole life.
Literal
She [topic-は] lifetime single [remained-のまま] was.
~のまま attaches to a noun (here 独身, 'single') and gives 'in the state of being X / remaining X.' Combined with だった ('was'), the construction reports a static, unchanging state extending across the relevant time frame — her entire life. The の + まま combination is the noun-attaching version of the verb-attaching ~たまま; both convey the unchanged-state semantics. A neutral, biographical-feeling phrasing — softer and less performative than constructions like 独身を通す ('persist as single'), which spotlight the deliberate choice.