Expecting a cold shoulder from my cousin at her wedding?

So she got completely irrational over the shoes that I was supposed to wear as the bridesmaid. She acted like a little spoiled brat even though I tried to be calm and collected when talking to her, she is a college graduate and acted like a 2 year old. I tried so hard to negotiate with her but she decided to make it a big deal. Now she is very upset with me cause her mom chewed her out for being egotistical and telling me that I acted immature and that she was surprised that I'm not more grown up. She will be very cold during the wedding I suspect and I'm really thinking of just cutting her off after the wedding. I cannot believe that my cousin would put some pair of shoes before her own blood. So how do I prepare myself to the coldness that I will experience?