Toxic "friend", help?

So yesterday I found out that my "friend" had showed her sister, which is like 24 years old, screenshots of private personal messages I've sent her because I've trusted her. Plus we've been friends for over 3 years.
The messages were about my depression and anxiety and my struggle with family, and basically my suicidal and homicidal thoughts.
So now her sister messaged me not to speak to my "friend" and that she will be coming by my house to talk about it with my mother.

By the way I've told my friend that when I'm ready Ill speak to my parents about it, and she promised me she'll keep it secret. So there wasn't much need for her to tell anyone because I was planning to talk to my mother about it in private without any problems. So now I've got to deal with this whole thing, I'm literally shaking.

I need help, I need someone to tell me what to do because I'm scared because I don't want my mother to find out this way.
My "friend" has blocked me on everything and I don't know the sisters number.

So please someone help?