。
She'll surely capture John's heart.
Literal
She [topic-は] John [genitive-の] heart [object-を] capture [probably-だろう].
心をとらえる, literally 'to catch/seize the heart,' is a set figurative phrase for winning someone over emotionally — captivating them. The verb とらえる (also written 捕える, 捕らえる, 捉える) ranges from physical capture (criminals, prey) to mental grasp (meaning, essence) to emotional capture, as here. だろう adds the speaker's subjective probability — 'probably / I'd bet' — without committing to certainty. A natural blend of romantic optimism and gentle hedging that you'd hear from a friend speculating about how a date or first impression will go.