It's really strange isn't it, no matter how much she may hurt you, you can't hurt her. I wonder if this is because you arn't able to show that you are an emotional person to her, the times she betray you did you let her know how you felt? Or pretend it didn't bother you. If this is the way it is, it's why you can't tell her you don't want her at your wedding because she has stripped you of demonstrating emotions to her, and not wanting her their is showing her that things do bother you.. If that makes sense. Call her and tell her the wedding is off just before she sets off to attend.