。
She thinks of him as her benefactor.
Literal
She [topic-は] him [object-を] benefactor [as-だと] is-thinking.
恩人 ('benefactor') is built from 恩 ('debt of gratitude, kindness received') + 人 ('person') — someone you owe a debt of gratitude to, often for substantial help during a critical time. The full Xを Yだと思っている pattern marks an ongoing standing belief — 'she has the settled view that.' The ている here keeps the belief active in the present; contrast with the past ~だと思っていた, which often signals a belief once held that has since changed.