Dana Reeve coughed for a year before she knew why. She never once thought of lung cancer. She had never smoked. The cancer threat never entered her mind, so she tragically did not take the cough too seriously, she said in one of her last public interviews. Older men with voices turned gravelly by decades of heavy smoking get lung cancer, most of us assume. Certainly not young women who have always shunned cigarettes. How wrong we are. Dana Reeve died Monday, six months after she learned her cough was caused by the worst of all cancer killers, lung cancer. It was an unimaginable and seemingly unfair event, occurring just two years after she lost her paralyzed husband, actor Christopher Reeve. Dana Reeve was 44….