。
She likes listening to music.
Literal
She [topic-は] music [object-を] listen-to [thing-こと] [subject-が] like.
When 好き applies to an action, the action must be nominalized first — Japanese can't directly say 'likes verb-ing.' こと does the nominalization here, turning 音楽を聞く into 音楽を聞くこと ('the act of listening to music'). With more concrete actions, の sometimes substitutes (聞くのが好き), but with general statements of taste こと is the more common, slightly more abstract choice.