。
She wouldn't let go of her child.
Literal
She [topic-は] her own child [object-を] did-not-let-go.
手放す (literally 'hand-release') is a rich verb covering both physical 'let go of (something held)' and figurative 'part with, give up, surrender' (an asset, a possession, a person one is attached to). With a child as the object, the figurative reading dominates: she wouldn't be separated from her child — perhaps refusing to surrender custody, or simply holding on tightly through some hard moment. Past negative 手放さなかった is decisive: it didn't happen.