I don’t think your stepdaughter is doing anything strange at all. Perhaps you are misinterpreting it because you feel uncomfortable? It sounds as though she is simply wearing a towel after showering and before getting dressed for the day- in the privacy of her own home. I’m not sure why you think this is about you? Unless there is something more to the story that you have not shared? In my house growing up I often wore a bathrobe to walk to ththe kitchen to get a glass of milk or an energy bar before getting ready. Sounds pretty normal to me.