Individually, they’ve all found success. The breakout star Morris (of the pop smash “The Middle”) earned her second country radio No. 1, “Girl,” the day after the Newport performance. Hemby, one of Nashville’s most sought-after songwriters, recently had two credits on the soundtrack for “A Star Is Born.” Carlile is a veteran singer-songwriter who just won her first three Grammys, including best Americana album, for “By the Way, I Forgive You.” (Hemby calls her “Grammy Carlile.”) Shires, a vocalist and violinist, has been a cornerstone of Americana music since first playing with the Texas Playboys at 15.

But together, they’ve decided, they’re better — especially when it comes to confronting the daunting task of helping women succeed as artists in country.

The genre has a stark gender imbalance. “It’s the eternal question that no one’s figured out,” said Morris, 29, picking at eggs Benedict. (“Tomato-gate,” a 2015 controversy sparked by a remark about women being the tomatoes in country radio’s salad, has been followed by statistics indicating the percentage of women on country airplay charts is in steep decline.) “Everyone blames somebody else. It’s the labels, it’s the radio, it’s the publishers that don’t sign enough women writers …”

Shires, 37, added, “And radio will blame the audience.” The Highwomen concept was her idea, inspired by an informal research project: While on tour, she wrote down every song she heard on the radio to see if most were by men. Shires found not only that most songs played were by men, but when she called to make requests, she was directed to station Facebook pages where songs by female artists were pitted against each other in polls. Only one could win.