It's not about "who cares, she's only 4". At my wedding, I had simple clean white roses. And the groom, the best man, and the two page boys had them as buttonholes, and the bridesmaids and flower girls had them clipped here and there. It identified us as the wedding party. It was to separate us in photos, it let other guests know who was who if they were extended family. My aunt and her whole immediate family (8 of them) decided to order their own corsages. Pink and white roses with fussy bits. They didn't match, they didn't go with my deliberately chosen look, it's the one day the bride and groom get it to look how they want. They looked like they wanted to be seen as wedding party, it pissed off my other aunt because she thought they looked more included. It's really bad etiquette to dress your child in a flower girls outfit if she's not part of the wedding party. Don't even ask the bride, if she's too polite to say no, she'll be annoyed internally. This is their day, you shouldn't be dressing her up as a flower girl (in a different dress to the actual flower girls) at a wedding where she is not one.