Aw, no wonder your cousin is so excited! What a pleasure.....
I think her and your sister will look fab, dark red dresses sound lovely. Have you any idea of what style of dress yet?
I haven't any advise on dealing with dress fitting for someone who lives abroad, but I think Bianca's advice sounds great. Hopefully as well, it wouldn't cost too much to send the dress either...
Take care, Karen xx
