DD is 9. Since day 1 of reception has been best friends with A.
It's a small school and they have two parallel Yr R and Yr 1 mixed classes which go into Yr2 Yr 3 mixed class with the same kids. So for 4 years Dd has been with the same kids in her half class. She and A have been inseparable and two other girls (J &S) have always paired off and the other girl has always been best friends with one of the boys in the class and has never really played with the other girls. Until now there have been no squabbles or anything. Her class has been a dream compared to my other DC's!
In Year 4, they stop with the mixed classes and put both half classes together...
There are fights every break time. DD has always said it's the others who are fighting over who gets to play with her and she's tired of being the one who has to choose and always upsetting someone.
This sounds too good to be true, but apart from a badly worded "you can't play with us" once to A (she meant A couldn't play if she didn't want to play what they were playing) DD really doesn't seem to have done anything wrong.
I was a bit 
but a few discreet enquiries with two other parents and one class teacher corroborates this.
E.g. they have to choose partners for a lesson. S wants to go with A, but J wants to go with S and A wants to go with DD. S and J start arguing, they all get sent out, no work gets done.
There have been a couple of instances when DD was playing with J at break, A wanted to play with DD so they said she could join in. But then A won't speak to J and DD feels stuck in the middle.
Today it was DD, J and M playing. A wanted to play with Dd and ended up A arguing with J whilst DD and M at and watched. DD agreed to play tomorrow with J and M. But she also agreed to play with A because she didn't want A to be upset. So she cried herself to sleep because she was trying to be nice and now there's going to be an argument tomorrow.
With me so far?! There are 5 who in some combination argue over who plays with DD. Why they can't all play together is beyond me! So far, I've been saying she has to sort this stuff out herself, go play with the boys (No!) ask to join in with football, ask to play with our neighbour (who she plays with all the time out of school, it doesn't seem to talk to in school as she's from the "other" half of the class [rolls eyes] ).
I don't know what else to say to DD.
I've suggested "we're playing X do you want to join in" so the onus is on the child who wants to do something different to say no.
Is it time to contact the school?