Setsuna is really wearing platform boots XDDD And lmao, I think that's true too. The novels has illustrations of dressTieria, so does Blue Bonds, and now this one too.

I was thinking they may have gotten it via Wang Liu Mei, but she herself didn't know that Tieria was going to wear a dress. Then again, all she did was to tell them that there was going to be a party. Imagine what she'd think if Sumeragi asked her for a dress, stockings and high heels. XDDD Or maybe she would have thought that one of the girls, along with one of the Meisters, were going undercover.