。
She's worried about his safety.
Literal
She [topic-は] his [genitive-の] safety [object-を] is-worrying.
心配する takes its worried-about thing directly with を. Here the object is 安否 ('safety, well-being,' literally 'safe-or-not'), a Sino-Japanese compound that captures the question itself — 'is he safe or not?' The phrasing 安否を心配する fits situations where someone is missing, in danger, or out of contact — distinctly different from worrying about general health (健康 / 体の具合).