My mum shouts all the time.. Without reason?

First of all, I am transferring schools but since I am also moving in a month, I'm going to be home-schooled until the move so I am at home all the time.

This morning I tried to wake my mum up because she had to take my little sister to school, however she wouldn't wake up. So at 9am (the time my sister's school starts) she finally woke up but started shouting at my little sister for not waking up and getting ready when it was her own fault. Then she started shouting at me for not waking her up, even though I did three times.

It's like this every morning. If they're not late, she would be shouting at the fact that my sister is taking too long to out her shoes on or that she can't find her phone.

In the afternoon, she's okay, sometimes anyway but if one small thing goes wrong, she will just shout without asking what happened or trying to solve it. When she shouts, it goes on for at least 10 minutes and she says stuff like "I'm going to kill myself.", "You're all so f***ing evil, you're doing this on purpose aren't you? You want me to die." and also "I can't take this anymore. I don't want you to life here anymore. Why do I get the messed up daughters when everyone else has the good ones?"

My parents are divorced and my dad remarried however, I don't think that has an affect with this since this happened a while back and she has been fine for ages. She has started shouting again like she used to and I cannot handle it. I don't know what to do.