The context of that passage is that it was quite odd for Selucia herself, as so high ranking Da'covale, to take on the more menial task of not only helping to choose Tuon's wardrobe for the day, but actually dressing Tuon herself. It's simply meant to illustrate how devoted Selucia is and how jealous she is of Tuon's person. She is so devoted, that she views it as a special thing; it has nothing to do with whether she is property or not.