I agree that there may be nothing you can do. But I do think it's good that you are showing that you are not changing as a friend. Let it be her who cancels the friendship, not you. That will show the error of the shunning practice and may some day spark some independent thinking in her mind. I have friends who are now avoiding me since I stopped going, but I make a point to act exactly the same and show them that I still want to be friends. I want it to bother them that they are the ones supposedly righteous, but I am the one who is being a true friend.