Dear Annie: I have never written to a columnist in my 70 years, but “Sad and Somewhat Angry Granny,” whose daughter-in-law wouldn’t allow her kids to open any of the Christmas gifts Granny brought them overseas before Christmas Day, really struck a chord with me. What a wonderful opportunity her daughter-in-law missed to model flexibility, kindness and care. Those grandchildren, ages 3, 6 and 9,…