Hey, the poster had said you don't even need a costume, so Harley having one already put her in Liliana's good graces.

"Harley, darling, hello," Liliana said. "I have no idea what your costume is--" and was only about eighty-three percent sure it was a costume, having met Harley before "--But I'm so glad you could make it. O trust we've lived up to your expectations."