My mom is abusive because she is mentally ill and she refuses to admit it/get help?

My mom has some sort of mentall ilness im sure if it but she refuses to get diagnosed. I promise im not making this up. I believe she has biopolor disorder coupled with some sort o narcissistic personality disorder. Even my dad knows jt. All of her friends realize it and then stop being her friend. Im 18 in a few days and it took me so long to realize that she is the problem, not me. She loves putting me down. She has completely destroyed my confidence and self/esteem. She has no moral compass and only thinks of herself and when she DOES think of me or my sister, she tells us the only imporant thing in life is to be popular, that if we "be ourselves" we will fail. She hates me and has told me she wanted to kill me with her bare hands and wishes i was never born. She even claimed i "wasnt her daughter." Its ok because i dont really see her as a mother. She has beaten me up with complete loss of control. Everyone around her avoids her. Its gotten to a point where i can honestly say i dont love her. I jusy want her to get help so that she can stop hurting everyone around her. My dad wont do anything. I feel like i cant talk to school counselors. Im honestly lost. I will be out of this place soon but i worry for my sister. Advice?