彼女が歌っているのが聞こえた。

she; her; her; girlfriend; sweetheart

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to sing; to sing (one's praises in a poem, etc.); to compose a poem; to recite a poem

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

to be heard; to be audible; to be said to be; to be reputed