Faith Hill isn't the only woman taking country's high road. Iris DeMent's debut record, 1992's Infamous Angel, revealed a pure voice with a timbre sharp enough to cut glass, giving her folksy tunes an authentically rural feel. Shelby Lynne is country music's comeback kid. After three formulaic major- label albums, she went over to tiny Morgan Creek Records and released 1993's stunning Temptation, a bluesy big-band romp that finally established her as a big-league contender. Martina McBride was just another pretty Nashville face until her second album, last year's The Way That I Am, intro- duced a punchier sound and a new, uptown look. The result: two Top 40 country hits, ''My Baby Loves Me'' and ''Life 9.