。
She swam across the wide river.
Literal
She [topic-は] wide river [path-を] swim-and crossed.
泳いで渡る is a te-form chain marking means: 'crossed by swimming.' This is a typical Japanese pattern for combining manner with action — same logic as 走って逃げる ('escape by running'), 歩いて来る ('come on foot'). The particle を on 川 marks the water as the path traversed, not as an object — same を-with-motion-verbs use as 道を歩く ('walk along the road'). The adjective 広い ('wide, broad') applied to a river suggests both physical breadth and the effort of the crossing.