。
She's just about to depart.
Literal
She [topic-は] precisely depart [about to-ところ] is.
The dictionary-form verb + ところだ frame marks an action right on the verge of happening — the moment just before. まさに intensifies the imminence to 'right at this very moment / just now.' The closing である is the literary copula, stiffer than だ or です — at home in writing, narration, or formal description rather than dialogue.