Help, please.

My sister thinks no one other than herself has depression. I've had it for about 8 years, probably longer and so do other family members. Even my mom is having a hard time because my sister's caused so many issues. She just said she wants to kill herself and we're not sure what to do. She's making her life harder and having depression makes you blind to these things. She fights with my mom everyday and we're so tired and hopeless at this point. 😩 she does drugs constantly, I'm afraid she'll move on to cocaine and popping pills soon. I went to a psychiatric center and it didn't help but maybe if she goes to a better one then it will? Ugh I worry about my mom so much, she doesn't deserve this. My sisters dad makes matters worse so we can't even take her there. We have no one to turn to. What would you do? I'm open to any suggestions