For nearly a year, Ariel Kempf was a server at a very busy breakfast and lunch café in Portland when, one day, while playing with her dog on the beach, she tore several tendons in her right leg. She had no health insurance, so she went to an urgent-care clinic where she was told she couldn’t put pressure on her leg for at least ten days and that it might take up to six weeks to heal. She had no sick days. Without delay, she called her coworkers who agreed to cover her next few shifts. She hoped to return in a week or so. But when the busy weekend came around and nobody was available to cover...