What should a grown up 12 year old girl wear to a wedding?

a suit or A tuxedo.

Answer:

Depends on the setting, the theme and his role in the wedding.

For most traditional weddings the wedding party men wear tuxedos, dark suits or kilts. Guests wear suits, dark blazers, or dark sports jackets.

For other types of weddings, and on the bride's request, the variety is endless