Are we unfair?

Are we unfair for not including my fiancé’s sisters children in our wedding party (page boy, flower girl etc..)? We wanted our little girl to be the only flower girl so she feels special on our special day and we chose my bridesmaid’s little boy to be page boy (he has to walk down the isle anyway because both his parents are in the wedding and he can’t sit on his own). His sister has said she is not coming to the wedding because of this. I think she is hurt because we chose our friends boy to be in the wedding and didn’t choose her children. Are we unfair by doing this? She has one boy and one girl.