。
She had never been heard speaking ill of others.
Literal
She [topic-は] others [genitive-の] insults [object-を] saying [nominalizer-の][object-を] been-heard fact [topic-は] did-not-exist.
A complex layered structure. 悪口を言う ('speak ill of, badmouth') is the inner verb phrase. ~のを聞かれる nominalizes that and feeds it as the object of 聞かれる, the passive of 聞く ('hear') — 'be heard doing X.' The whole becomes [embedded passive clause]+ことはない, the never-experience pattern (the negative of ~たことがある). Result: 'had never had the experience of being heard speaking ill of others.' Three verbs of saying/hearing nested inside one negative existential.