。
She'll probably get better soon.
Literal
She [topic-は] soon good become probably.
The plain ~だろう is the casual counterpart of ~でしょう, both signaling probability or expectation. Tacked onto the change-of-state 良くなる ('get better'), the prediction acknowledges the speaker doesn't have certainty but is reasonably confident. Useful in any context where you're offering an informed but unverified outlook — health, weather, scheduling, mood. The sentence reads as a calmly optimistic forecast.