I am so sorry to hear that you are going through this, I have a very similar story about my sister. So much of what you say is very close to home..
I was a wreck when I came here looking for advice, someone with a similar story that I could relate to, believe me I found it and took it , grabbed it with both hands! I really feel for you and urge you to try and find an Al-anon group near you. I, Like you, tried for years to fix things for my sister, making sure she got to her appointments and at times even making them for her...shes a grown woman!! Why was I doing this again???? trying to take control of the situation perhaps...yes! Till I realized I cant control it, just like you cant. I know my sister was capable of making those calls, the problem was..she didnt want to, simple! Its a sad but true fact. What I could control was the affect it was having on me & my life. It breaks my heart watching what this horrible disease does to my twin sister, and the rest of our family. But for now, I have stepped back & let her be the adult she is, to face the choices she has made. Doing all that fixing, trying to save her was keeping her in the place she wanted to be, with me to fall back on every day to pick up her pieces. Not allowing her to reach her rock bottom though I was rapidly reaching mine! I can see that now...I am always going to be there for her and told her, I am turning my back on her addiction not her...
I hope things get better for you Bella, there is always support for you here.