6 year old niece is literally going crazy in school

I’m posting this because my brother needs help. Okay so to start off , in kindergarten my niece was one of the best kids the teacher had. She constantly got different awards and at the end of the year she got a “ excellent student “ award... 1st grade came and well .. she is one of the worst students. ( she does her homework ) buuuut ... she behaves so bad and we don’t know why. Last week they evacuated class 4 times because of her. She was throwing stuff across the room, throwing chairs, hitting kids, she called her teacher a “ dumb dumb “ she has her good days but she’s had more bad than good. We tried telling her if she wants to switch classes and she screamed no. We asked if anyone is bullying her or calling her names and she said no. She did say that she wants her kindergarten teacher back because she didn’t really have strict rules in kindergarten than she does in 1st grade. Including you can’t bring toys to school. Which is her top rule she hates. But she needs to understand she’s going to have rules now. And plus, her kindergarten teacher is now a fifth grade teacher. My brother and SIL are so upset because they have tried everything. Oh and I forgot to mention, Saturday they took her to a pumpkin patch and she got on slides, rides and all that. She wanted to keep playing so they bought her more tickets and when they ran out again she threw a big fit because she wanted to stay there. She kicked her grandma and called her a “ dumb dumb “ as well and was screaming in the car “ help me, help me I can’t breath I’m gonna die “ ..... when my brother was telling me he cried and said he doesn’t know what to do anymore .... Today she acted up again in school out of nowhere in the last hour after they even said “ good job for being good today!! “ . they were able to sign her up in school counseling and we all really hope it works. But please if you have any advice for us, I’ll take it all !!!