。
She was awake all night.
Literal
She [topic-は] all-night eyes [object-を] is-keeping-awakened.
目をさます ('to wake up,' literally 'wake one's eyes') is the everyday wake-up verb, often written 目を覚ます with kanji. The kana spelling here softens the visual register. ~ている on 目をさます gives 'is in the state of having woken' — i.e. 'is awake.' The kanji form 覚ます shares its root with 覚める ('come to one's senses') and 覚える ('learn, remember'), all sharing the kanji 覚 ('awareness, senses'). 一晩中 ('all night long') is a fixed adverbial frame: ~中 ('throughout') stacks with time spans (一日中 'all day,' 一年中 'all year') to mark continuous duration.