。
She was absent from class.
Literal
She [topic-は] class [object-を] was-absent-from.
欠席する (けっせきする) is the formal term for being absent — more official and written than 休む. Where 休む is neutral and could mean skipping casually, 欠席 carries administrative weight: this is the word on attendance records and official notices. 授業を欠席した reports the absence as a recorded fact.