。
She put on a sweater.
Literal
She [topic-は] sweater [object-を] wore.
A minimal sentence demonstrating 着る — the verb specifically for putting on or wearing upper-body clothing. Past tense 着た describes the completed act of donning. Note that Japanese 着る has the same dual reading as English 'wear': it can mean either the moment of putting on (perfective) or the ongoing state (often expressed as 着ている). Here the plain past locks it into the perfective reading. セーター is from English 'sweater' via mid-century loaning.