。
She insisted on her innocence.
Literal
She [topic-は] her own innocence [object-を] asserted.
主張する ('to claim, insist on, assert') is the standard verb for vocally maintaining a position, especially in a dispute or legal context. 無罪 specifically means 'innocence' in the legal sense ('not guilty'), distinct from 無実 ('innocent of the accusation, blameless'), which is more about factual non-involvement. 自分の無罪 frames the legal status as her own — typical of court or accusation scenarios.