。
She'll be here soon.
Literal
She [topic-は] soon come probably.
~でしょう is the polite form of ~だろう, both expressing epistemic probability — 'probably / I expect'. The form sits in the gray zone between assertion and hedged prediction: not quite as confident as a flat statement but not as uncertain as ~かもしれない ('might'). With rising intonation the same form becomes a confirmation-seeking question ('she'll be here soon, right?'). Without rising intonation, as here, it's a confident prediction.