。
She bought six yards of cloth to make a dress.
Literal
She [topic-は] dress [object-を] make cloth [object-を] six yards bought.
The clause ドレスを作る (will make a dress) is a relative modifier on 布 (cloth) — the verb sits in plain non-past form to function as a noun-modifier. Two を particles appear because the inner one belongs to the embedded 'make a dress' clause and the outer one is the direct object of 買う. Yards rarely show up in everyday Japanese — fabric is sold by the meter — so encountering ヤード often signals a translated text or imported sewing pattern.