Erica Lafferty lost her mother on Dec. 14, 2012. The late Dawn Lafferty Hochsprung, then principal of Sandy Hook Elementary, was killed when 20-year-old Adam Lanza stormed into the building and fatally shot 20 children and six staff members, before shooting himself in the head. That was days after the final Thanksgiving she and her daughter would share. As Lafferty wrote in USA Today on Friday, “This Thanksgiving, I sat at a dinner table with an empty seat.