My sister has borderline personality disorder

I didn’t know what it was at first. I just saw her bipolar disorder at first where she would be sweet one breathe then turn mean in the next. She desperately tries to be an independant person not wanting anyone to worry about her, when we do. She doesn’t understand the concept of family and she doesn’t see the good, only the bad. I know she was diagnosed with Borderline Personality disorder but I didn’t know what that meant. It wasn’t until after looking into it, I realized this is why she attacked our parents verbally. Why she felt neglected. Why she feels things more strongly than others. Why her movie does not match up with everyone elses. Why she shreds our mom in viscous verbal attack in a fit of anger and how she falls to pieces devistated. I still don’t get the fully understand it, which is why I am here.