A writer launched into orbit by Oprah

'I'm in a one-day-at-a-time mode for most things right now." Ayana Mathis might well be. Recently the Philly-born, Brooklyn-based Mathis, 39, learned that The Twelve Tribes of Hattie (Alfred A. Knopf, $24.95), her first novel, the first piece of substantial fiction she'd ever published, had been chosen by Oprah Winfrey, goddess of all media, for Oprah's Book Club 2.0.