My fiancé and I would pay for it. I would cover expenses for my daughter. She wasn’t groomed for marriage per se. But she did receive instruction at an early age about proper suitors (gentlemen) and what that implied. This was well before puberty. And her lessons on character began even earlier.
Sewing a wedding gown is very labor intensive. I wouldn’t do it myself. But I would design it and oversee the work. I would make a few items for her trousseau like linens and items for the home. Maybe his and her sleepwear for them each.
You can put together a nice event if you have extra hands who are creative. This minimizes the costs. Someone who likes to cook, bake, decorate, do crafts, etc.