In Shoftim chapters 4 and 5 we learn of a woman named יָעֵל אֵשֶּׁת חֶבֶר הַקֵּינִי, Yael the wife of Chever the Kenite, who kills Sisra. In the song of Devorah, the Midrash (Ruth Rabba 1:8) and Gemara (Horiyot 10b) all seem to imply that she was Jewish, one reading has her as being a Shofeteth of the Jews (I'm not aware of anyone who claims any of the Shoftim were non-Jews), another expounds a moral lesson of the value of sinning for the sake of God (which she did by sleeping with Sisra).
I would like to know if there is an explicit source which states that Yael, the wife of Chever the Kenite was in fact Jewish.