DEAR MISS MANNERS: My younger sister and I have always been close. During our young-adult years, I took care of her, helping her clean up after the many reckless decisions she made. This included a large amount of time with her children staying at my home. They call me their “extra mom” now that they are adults. I love my sister, and she eventually turned her life around, becoming reliable, if still very emotional. Three years ago, one of her children died from an accidental drug overdose. This was devastating for everyone in my family — but for me, it was like one of my own children had died…