。
She was devastated by the sad news.
Literal
She [topic-は] that sad news [by-に] was-struck-down.
打ちのめす ('to crush, knock down, defeat utterly') in the passive 打ちのめされる describes being overwhelmed — emotionally floored by something. に here marks the agent or trigger of the passive action. The verb is built from 打つ ('strike') + のめす (an old auxiliary intensifier 'do thoroughly'), giving a vivid sense of being beaten flat. Pairs naturally with 知らせ ('news, notification'), 衝撃 ('shock'), 現実 ('reality') — anything heavy enough to floor someone emotionally.