。
She's a born musician.
Literal
She [topic-は] natural-born [possessive-の] musician is.
天性の ('innate / natural-born') is a Sino-Japanese compound meaning 'by nature' — 天 (heaven) + 性 (nature/disposition). 天性の音楽家 = 'a musician by nature,' implying talent that wasn't learned but is intrinsic. Stronger than 才能がある ('has talent') because it suggests the talent is fundamental to who she is.