What can I do about my mother who is emotionally abusive?

So, my mother is basically always picking on me and my sister. The minute we get into the car from being picked up from school, the complaining starts. She blames us for everything from her not having a job to the fact she doesn't like her clothes. We're always behind it somehow. She finds flaws in everyone constantly and calls us names all the time and it's getting worse. She makes me feel really bad about myself, continually searching for something else to pick on. She never holds back, im either "puting on weight" or "failing at school". But no matter how hard I try , nothing is ever good enough for her. She always picks on me most since im the oldest (15) and my sister is 12. She's divorced and jobless. I know not having a job is hard but it's not me and my sister's fault. She's so unpredictable aswell, you never know if she's going to turn on you at any minute. Im in a good mood, until I go anywhere near her, and Im instantly depressed. It's like she casts a black shadow over everything. I mean it's not like I don't have my own problems (which she always dismisses) I've just been diagnosed with type 1 diabetes and I have heaps of important exams coming up aswell as all the high school stresses to deal with. She always says stuff like im gonna get terrible grades and how im never going to amount to anything in life and how i'm going to be poor when I grow up, and it's really hurtful. You don't expect to hear that from your own mother! All my friend's mums are so nice, I envy them :( I've gotten used to completely ignoring my emotional needs and emotions because i dont feel safe expressing them when she's around. I also find it very hard to trust others. i realise now that all my problems in life (my insecurity, low self worth) Have steemed from her. Am i going to be scarred as an adult? What can i do to help both me and her?