。
She visited the teacher.
Literal
She [topic-は] that teacher [object-を] visited.
訪問する is the formal Sino-Japanese verb for 'to visit'; paired with 教師, the register evokes a courtesy call or a school memoir more than a casual drop-in. In everyday speech you'd more often hear ~の家に行った ('went to their house'), 会いに行った ('went to see'), or even 遊びに行った ('went to hang out'). 訪問 fits situations weighted with formality: official site visits, returning students paying respects to a former mentor, or a journalist's reporting trip.