。
She swam across the river.
Literal
She [topic-は] that river [path-を] swimming crossed.
A clean example of the path-を, where を marks the space traversed rather than a direct object. 泳いで (the て-form of 泳ぐ) acts as a manner adverbial: 'she crossed the river [doing-so by] swimming.' Two verbs link via the て-form to combine an action with its manner — a productive Japanese pattern: 歩いて行く ('go on foot'), 走って帰る ('run home'), 泳いで渡る ('cross by swimming').