。
She hurried down the stairs.
Literal
She [topic-は] stairs [path-を] hurry [then-て] descended.
急いで is the て-form of 急ぐ ('to hurry') used adverbially — 'hurriedly, in haste' — and attached to おりる it modifies the manner of descent. This adverbial use of the て-form (sometimes called the conjunctive use) is one of Japanese's main strategies for building 'do X-ly' phrases out of verbs: 走って行く ('go running'), 笑って答える ('reply with a laugh'). おりる is written here in hiragana rather than its kanji 降りる, a softer-feeling rendering you'll often see in less formal writing.