She said to him, "Please have a seat."

Literal

She [topic-は] he [to-に] 「どうぞお座りなさい」 [quotative-と] said.

A direct quotation marked by the 「」 brackets. お座りなさい combines the お~なさい imperative pattern — slightly polite-imperative, gentler than the bare ~なさい. どうぞ ('please, go ahead') softens the directive further, giving an inviting tone typical of greeting a guest.