וַתֹּ֣אמֶר אֵלָ֔יו בַּת־בְּתוּאֵ֖ל אָנֹ֑כִי בֶּן־מִלְכָּ֕ה אֲשֶׁ֥ר יָלְדָ֖ה לְנָחֽוֹר׃
Y ella respondió: Soy hija de Bethuel, hijo de Milca, el cual parió ella á Nachôr.
Rashi
בת בתואל DAUGHTER OF BETHUEL — She answered his first question first and his last last (cf. Avot 5:9).
Chizkuni
בת בתואל אנכי בן מלכה אשר ילדה לנחור, “I am adaughter of Betuel, who is a son of Milkah whom the latter bore for Nachor (Avraham’s brother). The reason she gave him all these details was that she did not want Eliezer to think that Betuel had been born by a concubine, but that he was the son of Milkah.
Or HaChaim
בת בתואל..אשר ילדה לנחור. The daughter of Bethuel whom Milkah bore for Nachor. Rebeccah emphasised that she was not the daughter or granddaughter of a concubine, but of the ranking wife.