oomis: all female guests at weddings wore gowns until recent years???? Not by frum weddings. Isn’t that how it works by goyim, were the female guests generally wear gown to a wedding or even a party like a “ball”? That’s were that idea comes from. But I don’t think that yiddisha weddings EVER had most female guests donning gowns. That would be pretty untzniusdik. Maybe in modern weddings its done differently. But I think the idea of mothers and sisters wearing a gown is an offshoot of that. I remember when the ONLY person wearing a gown at frum weddings was the Kallah.