Meet Erin McDermott before the gig, with a Guinness in her hand and a self-effacing wit at the ready, and you’d never suspect the transformation that’s about to take place. But when she sets down her pint and steps onto stage, pay attention. A spruce-topped six string launches into a steam-driving rhythm and her voice rises, gaining power and soaring to a pure quavering vulnerability that makes even the club regulars, the ones who’ve heard it all, stop talking and really listen. And why not? ...