。
She's a pianist.
Literal
She [topic-は] pianist is.
About as simple as a Japanese sentence gets — pronoun-topic + predicate noun + copula. ピアニスト is one of the routine Western-music profession borrowings: alongside バイオリニスト ('violinist'), ギタリスト ('guitarist'), チェリスト ('cellist'). Native words for these professions exist (例えば 演奏家 'performer, instrumentalist'), but the loanwords dominate everyday speech for Western instruments.