。
She should be here soon.
Literal
She [topic-は] soon come probably.
Polite probability prediction with ~でしょう. The slot fills the same role English uses 'should' for in scheduling contexts: 'She should be here soon' isn't a moral 'should' — it's an expectation based on knowledge of the situation. The polite ~でしょう form is the natural choice in any conversation where the desu/masu register is in play, whether business or polite social interaction.