Hey, that's a good question! It's unlikely that Ewok tribes keep human dresses around for just this sort of occasion. Where did they get that dress (screenshot below) that they gave to Leia?
There's good potential for a story here. Writers have done a lot with minor characters. One broken droid who briefly appeared at the beginning of Episode IV was turned into Skippy the Jedi Droid. Writers could tell the story of the woman who wore Leia's dress before Wicket and his friends ate her. Heck, why not make it a feature-length movie?