。
Whenever she has a spare moment, it's golf.
Literal
She [topic-は] free-time [even-さえ] if-exist-ば golf is.
暇さえあれば is a near-fixed expression that compresses the さえ~ば minimum-condition pattern into a unit: 'as long as / whenever (one) has even a moment of free time.' The さえ ('even') paired with the conditional ば creates the implication that just that one condition is enough to trigger the predicate. The wonderful comic effect of ending with ゴルフだ — without any verb — is pure Japanese economy: 'golf' alone, plus the copula, is enough to convey 'she's off playing golf.' Native speakers regularly use this verbless punchline pattern to sketch obsessions or habits with one syllable.