。
I hear she's been absent from school for a long time.
Literal
She [topic-は] the-whole-time school [object-を] is-resting [hearsay-そうだ].
学校を休む ('skip / be absent from school' — literally 'rest school') is the standard idiom for school absence; the を marks 'school' as the institution being rested from. The same 休む works for 仕事を休む ('take time off work') and 会社を休む ('skip work'). The hearsay ~そうだ at the end signals that the speaker is reporting what they've heard rather than direct knowledge — 'apparently' or 'I hear'. Combined with the ongoing-state ~ている and ずっと ('the whole time'), the sentence describes a sustained absence the speaker only knows about second-hand.