。
She looked at him with hatred.
Literal
She [topic-は] hatred [object-を] putting-in him [object-を] saw.
~をこめて ('put X into, infuse with X') is a productive frame for describing the emotional content with which an action is performed: 愛をこめて ('with love'), 怒りをこめて ('with anger'), 心をこめて ('wholeheartedly'). The te-form acts adverbially. 憎しみ ('hatred, hate') is the noun form of 憎む ('hate'). The combination 憎しみをこめて見る ('look with hatred') is a vivid descriptive phrase typical of fictional prose.