My daughter and niece are in the same class. My daughter is really struggling making and keeping friends, fall outs all the time. My niece has lots of friends, boys and girls, and although there are fall outs, she doesn't get upset like my daughter and the next day it seems to be forgotten.
I think my daughter and niece are quite similar so can't understand why niece is popular but my daughter is not. It breaks my heart to be honest.