。
She rejected his offer.
Literal
She [topic-は] his [genitive-の] offer [object-を] rejected.
拒否する ('to refuse, reject, decline') is a する-verb of formal flavor — common in legal, business, and bureaucratic contexts (拒否権, 'veto power'; 拒否反応, 'rejection reaction'). Compare with everyday alternatives: 断る (most general 'refuse'), 拒む (refuse with active resistance, often for nominalized clauses), 辞退する (politely decline an offer or honor).