。
She ordered a black tea.
Literal
She [topic-は] black-tea [object-を] ordered.
注文する ('to order') takes を for the thing ordered — used at restaurants, online stores, or anywhere goods/services are requested. Note the simplicity: a four-element sentence (彼女は + 紅茶を + 注文 + した) that nonetheless carries one cultural detail. In Japanese cafes, ordering 紅茶 typically gets you a Western-style black tea; if you want green tea, you'd ask for お茶 or 緑茶. The cultural lexicon for tea is split between Japanese tradition and Western imports.