、。
She said she was a pianist, but that was a lie.
Literal
She [topic-は] herself [subject-が] pianist [is-だ] [quotative-と] said [but-が], that [topic-は] lie was.
ピアニスト is a loanword borrowed straight from English 'pianist' — many profession names entered Japanese this way during the Meiji modernization, though the underlying instrument piano (ピアノ) is now perfectly naturalized. The clause-final が works as a soft 'but' connecting the two clauses; structurally it's the same particle as the subject marker, but functions here as a coordinating conjunction. それは picks up the previous claim as a topic before the verdict うそだった ('was a lie'). The flat past tense delivers the disappointment without melodrama.