。
She'll probably be able to swim soon.
Literal
[topic-は] soon can-swim probably.
泳げる is the potential form of 泳ぐ ('swim') — godan verbs form the potential by shifting the final う-row syllable to the え-row and adding る (泳ぐ → 泳げる, 書く → 書ける, 飲む → 飲める). でしょう ('probably, surely') is the polite speculative — softer and more polite than だろう, but functionally the same. The whole sentence is the kind of thing said about a child learning to swim — probably with a touch of parental pride. Schools in Japan typically include swimming in the summer P.E. curriculum, so 'learning to swim' is a near-universal childhood experience there.