She told her mother what she'd heard, over and over.
Literal
She [topic-は] heard thing [object-を] many-times mother [to-に] told.
聴いたこと ('what she heard') nominalizes the experience with こと. 何度も ('many times / over and over') emphasizes the repetition. 母親 is a more formal word for 'mother' than お母さん — used when talking about someone else's mother or in a descriptive, third-person context.