“Look at all I’ve done in 80 years. I feel like I’m just getting started,” Dolly Parton told People magazine in November. More than 100 million records sold worldwide, a sprawling business empire worth $450m (£334m), the set-in-stone title of the “queen of country” – “all I’ve done” seems an understatement when discussing the career of a woman who rose from impoverished Appalachian childhood to all-American icon.