。
She should already be at the office by now.
Literal
[topic-は] already company [at-に] arrived-is [should-はずだ].
~はずだ expresses logical expectation — 'X should be the case, based on what I know.' Stacked on 着いている (the resulting state of 着く 'to arrive'), it gives 'should be in the arrived state' = 'should already be there.' Distinct from ~べきだ ('should' as in moral obligation) — はず is purely about likely truth, while べき is about what one ought to do. Practical context: probably the speaker is wondering why she hasn't checked in yet — a common Japanese workplace pattern when a coworker is late and someone is trying to track them down.