。
She plays the piano very well.
Literal
She [topic-は] very skillfully piano [object-を] plays.
じょうずに is the adverbial form of the な-adjective 上手 ('skilled, good at'). The kana spelling じょうず in this sentence is informal but standard; the kanji form 上手 would also be common in writing. 弾く (here written ひく in kana) is the dedicated verb for playing string and keyboard instruments — pianos, guitars, violins, harps, cellos. Different verbs go with different instrument types: 吹く for wind instruments (フルートを吹く), 叩く for percussion (太鼓を叩く), and the Sino-Japanese 演奏する for any kind of performance. ピアノを弾く is one of the most basic music collocations a learner picks up.