When Sara Nelson agreed to come to Madison, Wis., to discuss the future of labor at an ideas festival on the University of Wisconsin campus in the fall of 2021, it was supposed to be just another appearance by one of America’s most engaged and energetic labor leaders. Then, Nelson, the international president of the Association of Flight Attendants, ended up having a pair of surgeries that required her to use a wheelchair for several months. Of course, she could have canceled the trip. But that’s not how Sara Nelson rolls.