。
She's of noble birth.
Literal
She [topic-は] noble birth is.
A pared-down version of the noble-birth construction: the noun 女性 ('woman') is dropped, leaving the noun-predicate 高貴な生まれだ to stand alone. Japanese drops elements freely when context fills them in. The plain copula だ instead of polite です matches the casual register; the elevated vocabulary 高貴な生まれ contrasts with the casual だ for a slightly clipped, novelistic feel.