Re: Hmmm :(
"It also probably doesn't help that her best (and, for a significant portion of her late childhood and most of her teen years, only) friend is a bit of an airhead who can't keep up in intellectual conversations."
We came to the conclusion that peer group pressure was a bigger influence than the home environment. It happened at an early age. I remember helping her father assemble a pink Cindy type camper van toy one Christmas. Her close pals were from a neighbouring family of two girls. They probably felt like sisters. It may also be that she retreated into a niche away from competition with her undoubtedly bright older brothers.