。
She glanced at us.
Literal
She [topic-は] us [object-を] glance look-at.
ちらっと is a 擬態語 (state mimetic) for a brief, fleeting glance — quick, perhaps furtive, and usually not lingering. It pairs especially with 見る ('look') to form ちらっと見る ('to glance, to take a quick look'). Compare with じっと見る ('stare, look fixedly') for the opposite extreme. The choice of mimetic carries a lot of nuance: ちらっと can hint at curiosity, suspicion, or surreptitious observation depending on context.