。
She was a blonde girl.
Literal
She [topic-は] gold-haired [genitive-の] girl was.
金髪 literally translates as 'gold-hair' — Japanese describes the colors of hair as compounds with the color word + 髪. Black hair is 黒髪, brown is 茶髪, white/gray is 白髪. The pattern noun+の attached to 少女 ('young girl') turns 'gold-haired' into an attributive ('gold-haired girl'). 少女 is a slightly literary word for a girl — typically pre-teen to early teens; the everyday word would be 女の子.