The outfit was not what Luna wore in her day to day life, but she had been living with Peitho long enough - and appearing on her website long enough - that she had gotten pretty used to costumes for the sake of sexual attraction.
You're doing this for Peitho, Luna told herself, remembering the distressed face of her goddess after Hermes was gone.
(Luna was unaware that Peitho had called Merlin a little earlier, unaware that the wizard had been told that Luna had had a very difficult last few days and that if he brought any harm to her, Peitho and Hecate would collectively see that he was never able to please himself with a pretty girl ever again. Be kind to her Peitho had told the wizard, both as warning and request. She is precious to me.)
Luna knocked on the door and waited, smoothing down her skirt. When she door open she smiled ever-so-sweetly at the older gentleman there. "Hello," she said, a slight tilt of her head. "You must be Merlin."