Step daughter picks out what to wear

My boyfriend's daughter 5 years old. Her mom lets her pick her own clothes to half the time to school. Most of the time she looks absolutely ridiculous. 

He is embarrassed by it. We picked her up today, and she had on pink polka dot tutu, Santa Claus pants, and a Halloween shirt with a feather vest, and sparkle shoes 

Her mom says she wants her know Its okay to be her own person. We are not okay with his child looking crazy at school. We went the store to buy a change of clothes because how ridiculous she looks 

What should we do so the mom knows its not okay to let our daughter dress like that to school or even ever?

"She said it's preschool... The kids don't care!"