。
She'll be back before long.
Literal
She [topic-は] before-long will-return [probably-でしょう].
でしょう attaches to the plain form to mark a confident prediction or speculation — 'probably will, likely.' Softer and more polite than だろう, with which it shares its function. Pairing でしょう with the literary-tinted ほどなく creates an interesting register clash: a written-flavored adverb with a polite spoken predicate. In practice this kind of measured politeness fits formal hospitality, business reception, or someone reporting on a guest's whereabouts.