Unfortunately both girls could not tell her anything except that they no longer wanted to be her friend. I think that she might have been smothering them - she likes having just one friend although that seems to be changing.
Her "popular" books mainly discuss looks. My daughter has noted that the blond girls are more popular than girls of color.
If I bring up alternate items to say, she just exclaims that she doesn't know why someone would not want to know this or that fact. We do work on this skill.
I do understand that it's a choice about emulation vs. jealousy - she is adamant about her opinion of her sister. I do follow the "Siblings Without Rivalry" method with limited success.
Thank you for your link.