“How can someone seem loving for years—then suddenly turn cruel?” This week’s Fan Mail revisits a letter that struck a nerve with listeners. A woman wrote about her daughter-in-law, who had seemed like a wonderful addition to the family for seven years—until she “suddenly turned into a monster.” But after the episode aired, Dr. Kerry received another listener’s response who offered the opposite perspective: “I was in a 23-year marriage marked by coercive control and escalating abuse. My in-la…