Basically the girl who has been her best friend since Yr 2 has dropped her, no other firm friendships are emerging for dd, she feels lost and out of place and was very upset yesterday, saying she doesn't understand why she isn't liked. 
I don't understand it either, the only thing I can think of is that she is maybe a bit more serious and earnest than the others, and she has the reputation of being "the brightest girl in the class", which doesn't seem to help with popularity.
She has now said she would like to go to a different primary school, where some girls go whom she knows from Brownies. I'm not sure whether to go along with this idea, or whether to encourage her to stick it out?