Undeterred and seriously determined to not have all that work gone to waste, I sat down and measured and drew a new pattern for a new BETTER costume and I made it on Friday. I'm happy to say that it fits her great with a little room to spare for the month of growing between now and Halloween. I'll wait to post pictures of her in it when Halloween gets here.
(The skirt is actually in a straight line and very symmetrical, but I took the picture from the side and flipped it, that's why it looks crooked!)