。
She gave us some useful information.
Literal
She [topic-は] us [to-に] usefully serves information [object-を] gave.
役に立つ ('to be useful,' literally 'stand in a role') is one of the most idiomatic compound expressions in Japanese — a fixed clause used attributively (役に立つ情報 'useful information') as easily as predicatively (この本は役に立つ 'this book is useful'). くれる is the inward-direction giving verb, used when *someone else* gives to the speaker or the speaker's in-group. Compare with あげる ('give outward') and もらう ('receive'). The polite past くれました situates this as recounted polite speech.