We had the exact same issue with DD1 last year at 4yo Kinder. (Did post about it last year, but sadly got no responses).

Spoke to the Kinder teacher about it and found out that she was not the only one having a few social issues. Seemed there were a few strong personalities, along with quiet kids, so there was a bit of conflict. Part of DD's problem, was that she was too polite, by asking to play first it gave the chance for the other kids to say no. If she just joined in with the play, it was all fine. Due to the number of kids having issues they decided to run a social skills course with someone from the children's centre at the council, it was a great help. Also half way through the year the kinder teacher changed and she was so much better. The first blamed DD a lot, whilst the other put some effort into helping, the whole class seemed to improve with the new teacher.

DD in particular has one frenemy. She would play well, then suddenly pick on her and say horrid things. It was awful, DD would be sobbing each night and it was hard as a parent not to track down the other parent and have a go at them. No matter how much we told DD that this girl was not a friend, she would just respond "but we are all friends at Kinder!" totally frustrating. Wish the first Kinder teacher had never started that rubbish. Had to spend a lot of time explaining that everyone need to be friendly, respect each other, but you don't have to be friends and if you are not friends, then don't be mean to that child. Thankfully the second teacher was of the same opinion.

DD still had issues going into Primary school, she still needed to learn about taking turns with playing, she would go off by herself if they did not want to play her game. Her primary teacher spent a bit of time getting through to her that whilst they may not play her game today, they may tomorrow. We made sure with primary school, that the main offender was in a different class (thankful the school was obliging there), it helped a lot get her away from the "frenemy"

Huge : hug: it can be so hard. Had me close to tears many nights.