I wa brought up to believe it was bad form to wear white but the last few weddings I've been to I've seen ladies wearing it, do you know the bride well, if so, ask her what she thinks.
This actually happened to me,and the person stood next to me only to be told by the photographer to go to the end of the group photo.So if she can change it that might be better for her.
Because opinions on approrpiateness of white vary so much, I would suggest erring on the side ofd caution. Better safe than sorry - I am sure your daughter would not want to feel uncomfortable on the day.
basically its ok as long as no-one could mistake you for the bride - so perhaps coloured shoes, bag, tights, jewellery, hat etc and maybe a jacket or wrap or something.