。
She said she'd be right back.
Literal
She [topic-は] soon return-polite [quotative-と] said.
Note the embedded clause is in the polite ~ます form: 戻ります. Quoted speech in Japanese typically preserves the original speaker's register — if she actually said it politely, the quotation reflects that, even though Japanese reported speech doesn't have to. Compare with the alternative 戻ると言った (using the plain form), which would either flatten the original register or report her informal speech. 戻る ('to return / come back') is the everyday verb for going back to a place one started from.