What do you think of me refusing to switch my daughters flower girl dress?
Wait, why would you not want to switch the dress?
The dress is extremely important to me. I don't think I'd be able to witch it even if I wanted to.
Weddings are very complicated events and while the dress is important to you, the wedding is very important to the people getting married. If they want her to wear a dress that goes with the theme of the wedding, you should be willing to change the current one or risk having her flower girl role taken from her.
I don't care, I didn't even like the wedding but this dress is important to me.
The dress may be important to you, but the event isn't about you and you need to keep that in mind. This os someone else's big day and they are going to want everything to be perfect. You being unwilling to change the dress could ruin the day for them.