。
She's thought to be diligent.
Literal
She [topic-は] diligent is [quotative-と] is-being-thought.
~と思われる is the passive of ~と思う — '(is) thought to be / appears to be.' This impersonal passive removes the thinker from the sentence and presents the judgment as a general public impression rather than the speaker's own opinion. The tone is hedged, even-handed — common in writing where the author wants to attribute a perception to 'people in general' without naming sources.