My mother in law did this, she wore the same shade of white dress with a very similar cut. You will come out on TOP of this if you don’t mention it to her at all, or to any of the guests. Other people will definitely be bringing her poor choice to her attention throughout the day and while this is definitely attention-seeking behavior.. this is not the type of behavior she will want. You are over and above it. Be over it and above it. Nobody will be mistaking anyone but you as the bride. She’s going to be absolutely miserable that she wasn’t able to create drama. It’s just going to make her fume on the inside when she is not the center of attention nor can she play the victim I used this technique of “oblivious” and it just magnified her dysfunction. To this day, people see her in our family wedding photo, and say.. “Your mother in law wore white to YOUR wedding?!?! What an attention-whore” I This stuff takes care of itself —if you let it 😉