。
She turned down the proposal.
Literal
She [topic-は] proposal [object-を] refused.
プロポーズ specifically refers to a marriage proposal — semantic narrowing from English 'propose' (which can mean any kind of suggestion). 断る ('to refuse, decline') is the standard verb across registers; the action targeted by the refusal takes を as a direct object. The terseness of this sentence makes it punchy — a clean dramatic beat.