I enjoyed making my children's Baptismal dresses and my sister's wedding gown--the children's were made with fine muslin and my sister bought her own heavy satin and lace. If I got hit with a request I felt would be more agony than pleasure, I would find a pattern or picture of appropriate dresses I felt were in my skill range and give DD a choice. IMHO I could not justify hugely expensive material for a one-time event. (I made my wedding dress, too.)
If DD can't give up the fantasy dress, go to a thrift shop and look at wedding gowns to repurpose. We quilters DO know how to cut things out and sew them back together.
We get these crazy requests because our work makes us look so talented. My husband also is the worst at this "Make me a boat cover, seat covers, covers for my fishing reels, pockets inside my denim jacket, a hood liner for my Chevy truck for the car show, etc."