Your wife can use any type of dress as per your wish. But she is supposed to completely covered her body, body structure, hairs etc while going outside. No any one else, except you is supposed to enjoy the beauty / sexy / attractive dressing of your wife. Please read Quran & Hadith regarding the Hijab of a muslima. You should read 25.Matrimonial section of Holy Quran in below link of Islamic life style.