。
She betrayed his trust.
Literal
She [topic-は] his [genitive-の] trust [object-を] betrayed.
信頼を裏切る is a near-set collocation: 信頼 ('trust, confidence') + 裏切る ('betray, double-cross') = 'betray someone's trust.' 信頼 is built from 信 ('believe') + 頼 ('rely on') and is the more solid, considered counterpart to 信用 ('credit, reliability'). Both abstract — distinct from 信じる (the verb 'to believe').