Wow....what an experience. I am having a similar one as you.
I agree with Patio...writing her a letter and tell her you how you feel may be the best thing to do. Apologize for the way you conveyed your "emotions" about your mother to her...but not for the way you feel about the shunning topic. YOU have a right to feel the way you do. Reinforce the fact that your sister has the same right and you "respect" her for her own opinion and you would like the same "respect" shown to you.
You then have cleared your conscience for handling your emotional outburst. You have done all you can do in trying to mend a heated conversation, your way of "wiping the slate clean" and wanting to move on with your relationship with your sister.
The next step is for her to continue the relationship. After all, it takes 2 to have a relationship.
I truly hope all goes well for you.
CodeBlue