The best thing I would suggest to your wife is to take what you want to wear at the beach, go to the beach for the first day and see what others are wearing and try to mix in with what they are wearing, if she sees others wearing a G String then she can wear it too, no issues then. If she doesn't see anyone wearing it and thinks that she would feel comfortable being the only one wearing it, then she can go ahead and wear it. It would also all depend on the atmosphere at the beach.