。
She plays the violin well.
Literal
She [topic-は] violin [object-を] skilfully plays.
上手 ('skilled, good at') is a na-adjective; its adverbial form 上手に attaches to a verb to describe doing something well. The same idea can also be framed with 上手 as a predicate adjective taking が — 彼女はバイオリンが上手です ('she is skilful at violin') — which is more about the trait than the act. The choice between adverbial 上手に弾く ('play skilfully') and stative ~が上手だ ('is skilful at') subtly changes the spotlight: action vs. ability. The polite 弾きます (masu-form) gives the sentence a generic, neutral register, the kind you'd hear in a polite description or introduction.