My friend, a jewelry designer, would like to give as her wedding present the necklace she's making for me to wear at my wedding ceremony. Is this unfair to my fiancé?

What a kind offer! And a very generous and meaningful gift. This is perfectly appropriate. And your fiancé does benefit, albeit indirectly–your wedding budget now has a little more wiggle room. Suggest to him that you take the sum you would have spent on jewelry and instead use it for something you’ll both enjoy, such as a spa day for the two of you during your honeymoon. Win win!