Mustery solved!
I had put it on some FB groups as well and this morning I had a message to call the costume shop. I spoke with the sweet lady who made this dress!
She said she couldn't remember the exact year but knew it had to have been over 20 years ago. For one season, Silver Dollar City had done a "Wedding at the Saloon" and this was the dress!
The dress had seemingly disappeared after that production season and she never knew what had happened to it until now, when it resurfaced on a rack at Celebration City.