Hi Cristasphoto, Well, I guess a welcome to Susan's is appropriate for a starter.
There will be others here who will come around so you won't be alone for long and may ask all the questions you desire from them. I am truly uncertain here as to what to say except that at least you are old enough to make your own decisions and you and your sister own the house. Don't realy know much about the law, I got taken to the cleaners by my ex, but that's nearly thirty years ago.
It would seem though that if youre mom is posing any kind of danger to either one of you, even if only in the form of threats physically or verbally, I would make preparations to have here removed from the house. It is your legal right if you and your sister own the house and she is a potential danger to the both of you, especially when she is using.
I know some about such drugs, It can potentially be a volatile substance. I had a friend who was on the stuff, I ended up having her three children in my care for two years after she was taken away, and I was just beginning my life full time as a woman.
Cindy