Kevin - your daughter is eight. She is a baby, a kid. If she wanted to wear a tutu, striped socks, a hockey jersey, combat boots and a silver crown to HER b-day party... well, that is a luxury you have when you are 8.
Who cares how your W wanted your daughter to look? Unless she showed up to her own b-day naked then tell your W to butt out.
You know what one of my FAVORITE memories (and one of my first!) from my childhood? The day AFTER my sister was born. I was 4. My mom called me from the hospital before my Gran and me came to visit. I was so excited because I picked out my own outfit (not so much my sister was born, lol!). Green shorts with white stripes, orange shirt, red high knee socks and white sandals. The photos of that day are SO funny because of how I look. See what I am saying.. if your kid wants to go to her b-day party wearing a getup like that then who is your W to tell you it is wrong? Do you get my point?