Make sure they look nice, you could go get a nice new pair for the occasion. I feel they should either be really nice looking to say she is laid back or completely worn out to say that she doesn't care what people think of her. What kind of dress is she wearing? What kind of converse does she want to wear? They have some cute new ones you can buy, you can even make those custom ones on their website for this! I have done that before but I haven't bought them yet but they are so cute!
It's an old idea. Its been done in Hollywood for decades. Model/actress Cybil Shepard wore orange converse while wearing a black ball gown accepting an Emmy award way back in the 80's.Classic story. The gown with the sneakers makes a statement, she doesn't need anything else.