The pasuk itself identifies Deborah uniquely as 'an isha nevi'ah' who judged Israel (Shoftim 4:4-5), and Megillah 14a confirms her status as one of the seven prophetesses of Tanach, deriving from 'eshet lapidot' that she made wicks for the Mikdash — a detail that explains her title rather than her judgeship.
The Abarbanel reads 'isha nevi'ah' as testifying to the perfection of her intellect and her spiritual preparation, which is what allowed the prophetic spirit to rest upon her in the first place (Abarbanel on Shoftim 4:4), while the Ralbag similarly ties her judging to her prophecy, since it was she who brought Israel back to Hashem and a navi was needed to rebuke them for wrongdoing (Ralbag on Shoftim 4:4).
The Malbim lists Deborah's attainment of prophecy as one of four conditions that had to converge before the redemption through her could occur, noting explicitly that earlier saviors/shoftim had not merited prophecy as she did (Malbim on Shoftim 4:4) — this is the clearest statement in the sources that her prophecy was exceptional among the shoftim.
Chazal themselves ask why specifically Deborah merited this when Pinchas ben Elazar was alive at the time, and answer that ruach hakodesh rests on a person strictly according to one's deeds, regardless of whether one is a man, woman, servant, or maidservant — this is found both in Yalkut Shimoni on Nach, Shoftim 4:42 and in Tanna DeBei Eliyahu Rabbah 9.
The Sefer HaChinukh addresses the halachic difficulty of a woman judging Israel by suggesting either that her rulings were not formal adjudication but advisory wisdom and prophecy, or that the people voluntarily accepted her authority, which is valid since monetary stipulations of acceptance are binding (Sefer HaChinukh 77:5).
Shoftim 5:7 records Deborah's own description of herself as having arisen as 'a mother in Israel,' and Chochma uMusar 1 p. 144 draws out that this very phrase, though not meant arrogantly, appeared to border on haughtiness and brought consequence, while Sulam on Zohar, Vayikra 328 reads her sole judgeship as itself a mark of shame for a generation that produced no man fit to judge the nation.
Steinsaltz on Shoftim 5:15 treats her combined role as judge and prophetess as what empowered her to appoint and direct Barak into battle, an authority flowing from both titles together.
Peninei Halakhah, The Nation and the Land 6:16 brings Rishonim who hold that the Torah's restriction on appointing a woman applies specifically to malchut, not to other forms of leadership, and that the nation's voluntary acceptance of Deborah's leadership as a judge was therefore unproblematic even on this view.
Among responsa, Igros Moshe YD 4:25 treats Deborah as a prophetess and judge whom the people accepted as leader specifically because of her Divine authorization, while questioning how far comparisons to her case can be extended; a companion responsum, Igros Moshe YD 4:26, likewise cites her as a woman accepted as judge whose authority rested on an exceptional ruling grounded in divine command, accepted by the people themselves.
