。
She was captivated by the qipao.
Literal
She [topic-は] that China-dress [by-に] was-captivated.
魅了される is the passive of 魅了する ('to fascinate, captivate, enchant'); the kanji 魅 (also in 魅力 'charm' and 魅惑 'allure') carries the sense of bewitching, while 了 marks completion. The に here marks the agent of the captivation — 'captivated *by* the dress'. チャイナドレス is the Japanese rendering of the qipao (Mandarin 旗袍 / Cantonese 長衫), the form-fitting dress with a high collar and side slits originally from Manchu Qing-era China and made internationally iconic by 1920s–60s Shanghai fashion. Japan adopted the dress and the loanword together; the 'china dress' label is a Japanese English coinage rather than a direct translation.