DEAR HARRIETTE: There’s a pretty large age gap between my sister and me. When my mom had me, my sister was 16 years old. I have been told that when I was a baby, my sister would take care of me like I was her own. But when I turned 4, my sister joined the Air Force. A couple of years later, she got married and had children of her own. I am so happy for her. She has it all: an amazing husband, beau…