Yes, her outfit in the pic is the dress you make from the quest.
The way it works now, as soon as you get to the camp for the first time (when it's officially the camp and you name it with Lyvia) the very first thing Imawyn does is want the new outfit. So before you even make sure she likes you enough to have the party, and then get the violin the MC has already made her that outfit.
So, with you already having the parties unlocked, there isn't a way to go back in time for you to get the quest. But you aren't missing anything with that, it just takes a lot of spider silk to craft.
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As far as the drum, I don't think you need to have completed step 18 to do step 19. But she won't dance without the drum.
Have a party and dance with Tia, end the party and she should talk to you about the drum.
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If you still have the old system, and don't have the options shown in my pic, your save may be too out of date for the new party system.
	
		
			
		
		
	
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((P.S. I don't have a good name for Liandra, the rest are pretty much my how I think of them. Tia swinging her tits and axe all day, Lyvia's best body part, Bianca obvious reasoning, Imawyn annoying me when I go in the tent to manage the camp.))