I'm feeling very sad for 8 y.o. dd.
She has been 'best friends' with a girl since nursery - and they do get on well most of the time, sharing interests and enjoying each other's company. But her friend doesn't seem as invested in the friendship as dd is and has said a number of hurtful things to dd2 over the years - this seems to have escalated recently.
Friend is by far the tallest girl in the class and is clever, popular & charismatic with a personality that verges on overpowering. According to dd, she is frequently casually cruel to other girls in the class. It seems to be 'her thing', and she always gets away with it. Dd, usually very buoyant and happy, is as low as I've ever seen her over it.
I'm going to have a word with class teacher (Y4) and invite some of dd2's other friends over to play. Is there anything else you would do?
(Am friendly with the mum, as dd1 and her older daughter are good friends too - don't want to jeopardise their friendship if I can avoid this.)