I’m so glad you have grandparents who are able to take you in during this difficult time. I think you know your mother is in trouble. I hope your grandparents can talk her into seeing a doctor. Sometimes behavior like this is actually due to a biological/medical problem. That’s the first thing that needs to be checked out, especially this is a new and sudden change of behavior. If she is medically fine, then she needs a mental health evaluation. You can’t make any of this happen. I hope, I hope that either your mom’s parents or her husband can.
I know the whole situation is terribly hard on you. You have every right to feel angry and scared and upset. I hope you can remember that no one acts like this because she wants to. Something is going on with your mother that she really can’t help.
The best thing you can do right now is to just love her, and focus on dealing with your own situation as best as you can. You can’t control what your mother decides to do. But you can control how you move your life forward.
Focus on finding a way to connect with new school mates. Join a club or team. Figure out how to do well in your new school. Please don’t be shy about asking teachers for help if you don’t understand their expectations or if you find you need a little extra help. Sometimes the subjects in a new school don’t quite match up with what was happening in the old one. This is hard but the way your wrote your letter makes me think you have what it takes to manage it.
I wish you well.