How do I stand up to my mom?

That really sucks. :( u can talk to me if u need to.
Well, if things really get steamy, I would suggest get out of the house. Talk to someone, whenver it´s u teacher of a total stranger (like a police officer) It´s not legal for your mother to threaten you. Spend as much time as u need outside, alone of with some friends, but try not to stay too long, u mother might get mad for having u outside the house for so long. DON´T wait till she really beats u before u go seek help, do it before something happens. And try nto to picture scenes of her dying, it can worsen the situation. Whenever those thoughts appear, just shut them off and think of something pleasant. Don´t think negative about everything. That´s how many people in (torture) prisons mostly get broken. Their capturers try to break them door making them hopeless.Don´t get hopeless, just remember that to every bad side there is a good side too. Whenver it´s your mother of the whole situation, there´always a bright side.Just think positive and don´t be afraid to cry if u need to.
Don´t forget, your mother is also going through hard times. Even though beating of threatening u is not the right way to handle stuff, she also has her problems and depressions, especially since her friend died. Cuting off comunication would frustrate her and most likely cause her to slip back into depression\agression, ect. I know it´s very hard to forgive her, but u don´t have to just forget the entire situation and pretend nothing happen! u know the old saying, "Time heals all wounds...." I wish u good luck and hopefully, u and your mother can restore your relationship. :)

u need to talk to her about your feelings. Do not yell of scream of cry. Calmy and respectfully tell her how u feel. Try to make her understand and if she still goes on with her ways, find professional help. If things still don't get better and continue to get worse, I think u should consider moving in with a friend/aunt and uncle/cousin/older sibling/gradparents. Maybe u two do need some time apart to figure things out.