I subbed for a kinder class in which one child with a strong personality encouraged everyone to shun one particular little girl. Everone else seemed to get how wrong it was, but went a long with the "leader" anyway. My heart absolutely broke for this girl. The mean girl was MEAN to her and made sure she was left out of all group play. It was awful.
I brought it up to the teacher, who was clearly aware and unwiling to intervene. I intervened and talked a lot about niceness and the whole class (minus bully) seemed to breathe a sigh of relief and settle into being nicer. I brought it up to the administration and they all already knew. Despite the whole school being in on it, I don't think her parents really knew. Kid was resiliant and the staff opinion was, "It doesn't seem to be bothering her too much."
The parents ended up taking the child to another school.
I would speak with the teacher and the administration of the school and see what their perspective is. Talk with the guidance counselor, too, as they have a lot of tools that they employ to help kids socially. Maybe teacher can pair your child up with someone who will include her and stand up for her.
I'm sorry you're going through this. (((hugs)))