。
She was deeply concerned about her son's safety.
Literal
She [topic-は] son [genitive-の] welfare [object-を] very worried-about.
安否 ('safety, well-being, welfare') is a Sino-Japanese compound 安 ('peace') + 否 ('no, denial') — literally 'safe-or-not.' Common in news contexts (安否確認 'safety confirmation,' 安否情報 'safety information') and in worried inquiries about people in dangerous situations (disasters, war zones). 気づかう ('to worry about, be concerned about someone's welfare') takes the welfare-target with を. The combination 安否を気づかう is a fixed collocation for the kind of concern that's too serious for casual 心配.