。
She's already left the office.
Literal
[topic-は] already company [object-を] left.
出る ('to leave, exit') is one of the staple intransitive verbs that takes を for the source of departure rather than for an object — the を marks the location being exited. Other examples: 家を出る (leave the house), 大学を出る (graduate from / leave university), 部屋を出る (leave the room). This is a useful counter-example to the 'を only marks transitive objects' rule learners pick up early. 会社 here means 'company' but in this context refers to the workplace — i.e., 'she's left the office (for the day).'