。
She was wide-eyed when she heard it.
Literal
She [topic-は] that [object-を] hear [and-て] eyes [object-を] round-made.
目を丸くする is a vivid set idiom — literally 'make one's eyes round,' meaning to widen one's eyes in surprise or astonishment. Body-part idioms are a rich genre in Japanese: 目を白黒させる ('make one's eyes black-and-white' = to be flabbergasted), 目をつぶる ('close eyes' = turn a blind eye), 目を光らせる ('make eyes shine' = keep close watch), 目を細める ('narrow eyes' = look fondly). The te-form 聞いて chains the hearing as the cause/sequence to the reaction — 'heard and (consequently) was wide-eyed.' Compact and image-rich.