Wow. First off, I'm a musician and I go to a music school and I can totally understand how damaging it is to have your mom call music a waste of time. My mom does that to me all the time and it's awful. I'm lucky in that even though she thinks it's a waste of time, she still pays my tuition because I suppose she considers the school prestigious enough that she can rub it in her co-worker's faces.

As for cutting off all ties with your family, why not? Really, if she is still a negative force in your life and you need time to heal, cutting off all ties indefinitely would probably be very beneficial. In a perfect world, I really want to never speak to my parents again after I am financially secure. My mom can't seem to ever stop emotionally abusing me even after I told her to back off.

I guess the only real advise I can give you is to never stop playing. I don't know if you are doing music now or not, but having a passion for music seriously helped me develop an identity, a sense of purpose, and a sense of value.

[EDIT] I reread your post and your mom kinda sounds like a mother with narcissistic personality disorder. I'm not a psychologist, but maybe you should google narcissistic parents and read about it. I dunno, if it sounds familiar it might give you some answers to why she mistreated you. Doesn't excuse it though.