HRTFT but I would be annoyed if someone wore this to my wedding. It's just rude to wear a big cream/ivory/white outfit to a wedding if you're not the bride. (Assuming a standard Western-style wedding where the bride wears those colours.) If I went to a friend's wedding and saw one of the other guests wearing this, then I would give them some serious side eye.
Usually the bride really stands out in wedding photos because of this. Having another "big white outfit" in the photos spoils this effect.
Get the photographer to tint her outfit so it looks pastel pink or blue.
And never forget the power of an accident involving a big glass of red wine if somebody is really being a cheeky fucker with their wedding guest outfit.