She helped her daughter get ready.

Literal

She [topic-は] daughter [possessive-の] getting-ready [object-を] helped.

身支度を手伝った — 身支度 (みじたく, 'getting ready, dressing') is a compound of 身 ('body') + 支度 ('preparation'). 手伝う (てつだう, 'to help') takes を.