。
She left early, so she should be there by now.
Literal
She [topic-は] early left [because-から], around-now [contrast-は] there [to-に] has-arrived [expectation-はずだ].
Two grammar points chain together here: から states the reason why (she left early), and はずだ expresses what the speaker expects based on that reasoning. The key layering is 着いている + はずだ — 着いている marks the resulting state of having arrived, and はずだ wraps an expectation around that state: 'should be in the state of having arrived.' The は after 今ごろ carries a contrastive nuance — 'by this point, at least.'