。
She graduated from high school last year.
Literal
She [topic-は] last-year high-school [from-を] graduated.
Japanese marks the institution one graduates from with を, not から: 大学を卒業する, 高校を卒業する, 中学を卒業する. The logic is similar to 出る — leaving a place takes を rather than から in modern usage, treating 'graduate' as a kind of departure verb. 高校 is the standard short form of 高等学校 ('senior high school'), covering grades 10–12 in Japan. Graduation in Japan is a major social ritual: ceremonies in March (the school year ends in spring), the symbolic 卒業証書 diploma roll, the second button (第二ボタン) traditionally given to a younger admirer. After 高校, paths fork sharply between university, vocational school, and direct employment.