I have been thru something similar with my mom. We have had several disagreements over the years concerning my 3 addicted siblings. I have gone several long periods of time of not talking to her at all. Alas I decided that I wanted a relationship with her and that I would have to keep to my own personal boundaries in order to keep from going crazy when I did relate to her.
Finally I accepted that she is going to do what she wants to do regarding my siblings. Guess what just recently it all came to a head for her and I was able to be there for her. I never thought I would see the day when she would become totally fed up with them but she did. I am very thankful that we have a relationship cause I really do love her.
You can come to terms with your mom. Stick to your boundaries with her and do things with her that bring you joy and things will get better between you.