I've tried to remedy the situation and so far it hasn't moved forward. I will keep trying, hopefully this will be resolved soon. Thanks for all your input!
I strongly recommend that you let him bring her. Remember, you do not have to interact with her very much that day beyond thanking her for coming to the wedding, so it doesn't really matter that whether you know or like her. I agree that she was rude to say what she said to you, but excluding her from the wedding on those grounds will not solve anything; in fact, it would only make her more hostile toward you and potentially alienate FI's friend, especially if the relationship gets serious.
Re: What would you do?
Thanks for all your input!