Have to wonder what personal problems your mom is dealing with/finding herself unable to deal with, that's causing her so much pent up anger. Sounds like whatever it is, your dad's found himself unable to help, has gotten tired of trying, and has decided to take on the role of passive observer. Either way, the fact that you're here trying to find answers from people with similar experiences shows that you're intelligent and level headed enough that you may be able to make a difference.
What I'd do if I were you, find a time when she's not actively flipping out over something, say that you want to talk to her before things get too hard between you, specifying that if she starts attacking you, the conversation's over. Sit down with her, just the two of you, and explain your position to her. Let her know how you feel, but don't get abrasive with her, if you can't keep your own words civil, there's no way she'll be able to. Don't just accuse her of treating you as she does, explain how her treatment feels. Rather than "you treat me like I'm worthless", say "the way you treat me makes me feel worthless" (or whatever you want to say)
Ask her why she's always angry with you, etc. Explain that you love her, that you don't want to lose her, but that with the way things are going, you can see your relationship with her going past the point of no return. Try to get her perspective, and find out what it is that causes her to be so angry. It won't likely be something you can help with, but maybe she's been unable to express it to anyone, and just getting it out could in and of itself be a huge help.
Worst case scenario, you find out that she never wanted to be a parent, or had ridiculous expectations of how her child would be and is disappointed, either of which at least give you a strong stepping point for getting away from her asap.
Best case scenario, you find out that her anger comes from reasons outside of you, have given your mom someone she can talk to. Might even turn out to be something you can help with, like, lets say, your dad is distant, they never talk, she has no friends outside the house, and is as such basically just lonely. On top of being someone she can talk to yourself, you can discuss her interests, and maybe help her use the internet to find groups of like-minded women in the area she could meet and form friendships with.
It's important to know that parents aren't just "parents". They're just as much people as anyone else. They don't know everything, they get hurt, they deal with what they can as best they can, and what they can't deal with can build up inside them. Some people have emotional breakdowns, some people keep it inside them and withdraw, some people can't keep it inside them but have it bubble up as anger, sadness, or other emotions. You can't expect them to be invulnerable.
Leastways that's my opinion, do with it what you will, but good luck with whatever you decide on.