My mother had spent six years carrying something I knew nothing about. I discovered it the day a stranger kicked her wheelchair in a crowded store. But when I finally learned why she'd kept it, I realized I'd misunderstood the worst day of our lives. The woman had been following us through the department store for nearly ten minutes. First, she'd muttered that some people would do anything for special treatment. Then she'd followed us to the accessible checkout. Where she loudly accused my mother of pretending she couldn't walk. Mom ignored her. That seemed to make her angrier. "You're not fooling anybody," the woman snapped. When Mom still didn't answer, she stepped forward and kicked her wheelchair hard enough to make the front wheels jump. For one terrible second, I thought Mom was going to fall. She grabbed the armrests and steadied herself. Then the woman pointed at her. "See? She can move when she wants to."...