9 year old daughter being being left out at school?

my beautiful smart sweet 9 year old keeps getting left out by the other girls at school. This year there is only 5 other girls in her cl and when 1 decides my daughter shouldnt be played with they all follow suit. I know they are just following the pact, but she comes home all upset that she has "no friends and nobody to play with" I really dont know how to help her handle this. She knows how loved she is and how special we think she is and we prayed that would give her the self esteem not to care so much about what other little girls do or say. But that's not the case. Next year she will have a lot bigger cl, i am just concerned about getting her through this year w/o it damaging her anymore. On occasion they also make fun of her for no other reason then just someone to pick on. Their favorite is just to exclude her though.