Dear Lakra:
This is advice my therapist gave me and I believe it applies here: leave the relationship between your mother and your sister to… your mother and your sister and stay away from it. Leave it to be completely between the two of them. Have your own relationship with your mother, do not discuss the sister with your mother. If she talks about her, change the subject, tell her you are staying out of it. Same when and if you talk to your sister.
Have a relationship with your mother, with your sister, if you so choose, a SEPARATE relationship with each. As far as the holidays, if your mother is the hostess, leave it to her. Stay out of it.
I feel very confident about this advice. When it was given to me and when I practiced it, I knew every step of the way that it was the RIGHT course of action!
anita