。
She tied up the package tightly with string.
Literal
She [topic-は] that package [target-に] firmly string [object-を] applied.
紐をかける ('apply / wrap string,' i.e. tie up a package) is the standard verb collocation for fastening with cord. しっかりと is a 擬態語 of firmness and security — doubled with the optional adverbial と. Wrapping with care — straight folds, neat string knots — is part of Japan's wider attention to careful preparation, the same cultural attentiveness you see in 包む (gift-wrapping), 風呂敷 (cloth wrapping), and the formal aesthetic of presentation that goes with sending or handing over an object.