Do you think of her as a best friend? If so then you should talk to her. Sometimes people are really just wrapped up in their own little world and don't think about it. Or perhaps there is something she has been meaning to tell you? If you don't talk, you'll never work through it.

If you honestly aren't going to talk, then ask yourself how you will feel if you miss the wedding. At that moment it's not about her or how she will react, it's about how it will make you feel.

Beyond that I have no advice, just hugs. I think it's awful that you are in this position and I would be beyond hurt if I were you.