Parent to Parent: Older daughter is pulling away from sister

Q: I have two girls who have been best friends forever. The oldest one will start middle school soon and thinks she is grown. She’s pulling away from her younger sister and it’s causing bad feelings between them. Should I try to help them with this transition or should I let them work it out on their own? From a reader: My older sister did the same thing. It was extremely hard on me to get pushed to the side, but it happened. I tried to keep up with her...